HELP!!!! 94 Disco Stalling in Drive

Okay, I need help real bad. I just had the LR dealer perform a $1,500 tune-up (plugs, wires, cap, rotor, and coil). The truck ran almost perfectly for a week after I picked it up. Then it started losing ALL power at low speed in drive only. It doesn't stall at idle, but only when I'm in slow traffic it seems to loose all power no matter how hard I step on the gas. As soon as I put it in nuetral it shuts off. It did it once a week before, but now it's more frequent. It did it 5 times yesterday. The interesting thing is it doesn't do it on the highway.

I took back to the dealer and they told me that the only code they get is a TPS sensor, and I MIGHT also need a fuel pump but they are not sure. I really don't feel like spending another $900 while they play this guessing game, so any suggestions I can get would be greatly ppreciated.

Thanks
Desperate BakerVO

Update

I had a Rover specialist check it out and he found that the distributor "pick-up" was malfunctioning. Took it back to the dealer and they have ordered a new distributor.