1997 F150, 4.6 engine.
Changed the two back plugs because they were fouled and the engine was hesitating during acceleration. It ran well for about a month, then the engine started hesitating during acceleration. The two back plugs are fouled again. What's going on? Could it be the coils?

It sounds like wires 4 & 8 are crossed at the LEFT coil pack.

The correct wire locations are:
Rt: 1/3
.....6/5

Lt: 7/8
.....4/2

Looking from the top of the coil packs.