I just bought an 89' 3/4 ton Suburban and at part throttle it cuts out severely. It doesn't ever miss it just drops down to almost idle and you have no power. If I get out of the throttle as soon as it starts doing it and then get back in it the tranny will down shift and it takes off. The previous owner swapped in a th400 and I wondered if I needed to change something in the computer or swap to a computer from a manual tranny truck since the 700r is computer controlled. It has a GM crate motor in it with around 20,000 miles on it I have done a tune up and put on a new TPS. Now I am out of ideas but I am starting to think it has something to do with the tranny being swapped. Any suggestions would be appreciated.

that sounds a lot like the problem i'm having with mine. had a 4l80e behind it, now sporting an nv4500. past a certain throttle point, it just bogs down to nothing.

If you happen to figure out what is causing it let me know because I am stumped. Somebody mentioned some type of solenoid on a th400 that affects the shifting, and mine doesn't have it if anyone knows what I am talking about let me know what it is and if it is needed or not.

This also happned to me, try disconnecting the EGR vacuum hose and see if that fixes it. For some reason my EGR solenoid was activating when it should'nt and was causing the part throttle stumble. Let me know if this works for you.