I parked it over a long weekend and it started acting up when I left for work last week.

1998 F150 w/4.2L V6 and 4R70W auto trans, ~120K miles
Trans oil(Mercon V) changed @ ~105K miles - no noticeable bad things like discoloration or burnt smells and level is correct.
No CEL light/codes - OD light works normally, no flashing

When shifting into reverse, slams into gear hard enough to stall the engine. When shifting into drive, shifts hard and the engine stumbles but does not die. Then, when taking off from a standing start, shifts up through the gears too quickly, getting to top gear by about 20 mph and stays there until shifting into neutral. I have to shift into neutral when approaching a stop in order to keep the engine from bogging down and stalling. Engine noticeably knocks when bogged down in a gear too high for the speed. Shifting into neutral and back into drive again starts the cycle over. Symptoms don't get any better over time. I managed to nurse it to work and back, 30 minutes each way, and it continues to exhibit the same behaviors.

I'm leaning towards a TPS issue, but ....... anybody have any thoughts on these symptoms?

 

What happens if you shift it manually between 1, 2, and D?

 

Shifting down manually forces those gear shifts. Then when shifting back to Drive and accelerating away from a stop, it quick shifts up through the gears again. My "nurse" mode was to kick it into neutral when approaching a stop and shifting into drive when ready to accelerate away form the stop. I've been avoiding reverse altogether.

 

Shift up manually too, for now. Start in 1 then up to 2 then to D to keep it from lugging.

It sounds like you have more than one issue. The torque converter isn't unlocking, and the PCM doesn't know what gear it's supposed to be in - that sounds like a speed sensor problem but that should throw a code. I suppose it could be TPS related.