2001 Ford Supercrew 4x4

I have a 2001 F-150 4x4 Super Crew with 122,000 miles. As I drive in 2x4, periodically I feel a jerking motion as if something is slipping. This happens more frequently when driving up an incline or a hill but on occassion does occur on fairly level ground. It seems to be getting progressively worse. Am I looking at my transmission or the rear end?

sounds like a coil is failing

I would agree with firebird. Two of my Ford pickups I had in the past displayed similar problems that I thought were the transmission, turned out to be the engine. I'd check the engine first.

Even tho the engine light isn't on, does not mean it doesn't have a code stored! Scan it...bet you find a coil misfiring. Common.