The $8 savings isn't stable — it's the part I'd push on.

Grocery price gaps are usually transient: weekly rotations, overstock, one store's inventory problem. So the decision isn't "should I always drive further?" but "should I go this week?" — which is easier because it's opportunistic, not habitual.

If the gap IS reliable, just switch stores permanently. The detour cost disappears.

The framing problem: most people treat grocery shopping as one recurring decision ("where do I always go?") when it's actually independent decisions each time — if you know the price gap in advance. Most don't, because they find out only after parking at the closer store.