diff --git a/components/WeeklyGrid.tsx b/components/WeeklyGrid.tsx
index a55c2a3..1e2eb89 100644
--- a/components/WeeklyGrid.tsx
+++ b/components/WeeklyGrid.tsx
@@ -1,4 +1,4 @@
-import React, { useMemo, useState, useEffect, useCallback } from 'react';
+import React, { useMemo, useState, useEffect, useCallback, useRef } from 'react';
 import * as XLSX from 'xlsx';
 import { CombinedKPIs } from '../types';
 import { pivotWeeklySalesData, WeeklyPivotRow } from '../services/dataProcessor';
@@ -196,21 +196,26 @@ const WeeklyGrid: React.FC<WeeklyGridProps> = ({ data, top50Ranking, onDrillDown
         });
     }, []);
 
-    // Calculate totals in a SINGLE PASS (O(rows) instead of O(weeks × rows))
+    // Calculate totals in a SINGLE PASS
     const weekTotals = useMemo(() => {
         const totals: { [weekKey: string]: { units: number, spend: number, gv: number } } = {};
-        // Initialize all weeks
-        weeks.forEach(week => {
-            totals[week] = { units: 0, spend: 0, gv: 0 };
-        });
+        const visibleWeeks = weeks;
+
+        // Initialize visible weeks
+        for (let i = 0; i < visibleWeeks.length; i++) {
+            totals[visibleWeeks[i]] = { units: 0, spend: 0, gv: 0 };
+        }
+
         // Single pass through rows
-        rows.forEach(row => {
-            weeks.forEach(week => {
-                totals[week].units += (row.unitsByWeek[week] || 0);
-                totals[week].spend += (row.spendByWeek[week] || 0);
-                totals[week].gv += (row.gvByWeek?.[week] || 0);
-            });
-        });
+        for (let i = 0; i < rows.length; i++) {
+            const row = rows[i];
+            for (let j = 0; j < visibleWeeks.length; j++) {
+                const w = visibleWeeks[j];
+                totals[w].units += (row.unitsByWeek[w] || 0);
+                totals[w].spend += (row.spendByWeek[w] || 0);
+                totals[w].gv += (row.gvByWeek?.[w] || 0);
+            }
+        }
         return totals;
     }, [rows, weeks]);
 
@@ -274,41 +279,36 @@ const WeeklyGrid: React.FC<WeeklyGridProps> = ({ data, top50Ranking, onDrillDown
 
     // 2. Sort results
     const sortedRows = useMemo(() => {
-        if (!sortConfig) return filteredRows;
+        if (!sortConfig || filteredRows.length === 0) return filteredRows;
 
         const result = [...filteredRows];
-        const metricKey = sortConfig.metric === 'units' ? 'unitsByWeek' :
-            sortConfig.metric === 'spend' ? 'spendByWeek' : 'gvByWeek';
-        const weekKey = sortConfig.key;
-        const direction = sortConfig.direction;
+        const { key: weekKey, direction, metric } = sortConfig;
 
-        result.sort((a, b) => {
-            if (sortConfig.metric === 'rank') {
+        if (metric === 'rank') {
+            if (!top50Ranking) return result;
+            const rankMap = top50Mode === 'eu' ? top50Ranking.eu : top50Ranking.uk;
+
+            result.sort((a, b) => {
                 const asinA = a.asin.trim().toUpperCase();
                 const asinB = b.asin.trim().toUpperCase();
-
-                let rankA = 999;
-                let rankB = 999;
-
-                if (top50Ranking) {
-                    if (top50Mode === 'eu') {
-                        rankA = top50Ranking.eu.get(asinA) || 999;
-                        rankB = top50Ranking.eu.get(asinB) || 999;
-                    } else {
-                        rankA = top50Ranking.uk.get(asinA) || 999;
-                        rankB = top50Ranking.uk.get(asinB) || 999;
-                    }
-                }
-
+                const rankA = rankMap.get(asinA) || 999;
+                const rankB = rankMap.get(asinB) || 999;
                 return direction === 'asc' ? rankA - rankB : rankB - rankA;
-            }
-            const valA = a[metricKey][weekKey] || 0;
-            const valB = b[metricKey][weekKey] || 0;
-            return direction === 'asc' ? valA - valB : valB - valA;
-        });
+            });
+        } else {
+            const metricKey = metric === 'units' ? 'unitsByWeek' :
+                metric === 'spend' ? 'spendByWeek' : 'gvByWeek';
+
+            result.sort((a, b) => {
+                const valA = a[metricKey][weekKey] || 0;
+                const valB = b[metricKey][weekKey] || 0;
+                if (valA === valB) return 0;
+                return direction === 'asc' ? valA - valB : valB - valA;
+            });
+        }
 
         return result;
-    }, [filteredRows, sortConfig]);
+    }, [filteredRows, sortConfig, top50Ranking, top50Mode]);
 
     // 3. Paginate
     const paginatedRows = useMemo(() => {
diff --git a/services/dataProcessor.ts b/services/dataProcessor.ts
index 8d41c7d..dfaf31c 100644
--- a/services/dataProcessor.ts
+++ b/services/dataProcessor.ts
@@ -1483,20 +1483,31 @@ export const pivotWeeklySalesData = (data: CombinedKPIs[]): {
     rows: WeeklyPivotRow[],
     weeks: string[]
 } => {
-    // 1. Identify all unique weeks and sort descending (YYYY-WW)
-    const weekKeys = new Set<string>();
-    data.forEach(d => {
-        if (d.week) {
-            const weekKey = `${d.year}-${String(d.week).padStart(2, '0')}`;
-            weekKeys.add(weekKey);
-        }
-    });
-    const sortedWeeks = Array.from(weekKeys).sort((a, b) => b.localeCompare(a));
-
+    const weekKeysSet = new Set<string>();
     const map = new Map<string, WeeklyPivotRow>();
 
-    for (let i = 0; i < data.length; i++) {
+    // Cache week keys to avoid repeated string formatting
+    // Key: year|week, Value: YYYY-WW
+    const weekCache = new Map<string, string>();
+
+    const getWeekKey = (year: number, week: number) => {
+        const cacheKey = `${year}|${week}`;
+        let k = weekCache.get(cacheKey);
+        if (!k) {
+            k = `${year}-${String(week).padStart(2, '0')}`;
+            weekCache.set(cacheKey, k);
+        }
+        return k;
+    };
+
+    const len = data.length;
+    for (let i = 0; i < len; i++) {
         const record = data[i];
+        if (!record.week) continue;
+
+        const weekKey = getWeekKey(record.year, record.week);
+        weekKeysSet.add(weekKey);
+
         const key = record.asin || record.sku || `${record.title}-${record.line}`;
         if (!key) continue;
 
@@ -1516,14 +1527,13 @@ export const pivotWeeklySalesData = (data: CombinedKPIs[]): {
             map.set(key, row);
         }
 
-        if (record.week) {
-            const weekKey = `${record.year}-${String(record.week).padStart(2, '0')}`;
-            row.unitsByWeek[weekKey] = (row.unitsByWeek[weekKey] || 0) + (record.unitsTotal || 0);
-            row.spendByWeek[weekKey] = (row.spendByWeek[weekKey] || 0) + (record.cost || 0);
-            row.gvByWeek[weekKey] = (row.gvByWeek[weekKey] || 0) + (record.glanceViews || 0);
-        }
+        row.unitsByWeek[weekKey] = (row.unitsByWeek[weekKey] || 0) + (record.unitsTotal || 0);
+        row.spendByWeek[weekKey] = (row.spendByWeek[weekKey] || 0) + (record.cost || 0);
+        row.gvByWeek[weekKey] = (row.gvByWeek[weekKey] || 0) + (record.glanceViews || 0);
     }
 
+    const sortedWeeks = Array.from(weekKeysSet).sort((a, b) => b.localeCompare(a));
+
     return {
         rows: Array.from(map.values()),
         weeks: sortedWeeks