I have a 1984 Ford Bronco II with a 2.8 V6 4spd manula OD that runs fines except under load. As long as it's not underload/in gear driving, it runs fine, but as soon as you let out on the clutch it's like you have shut off the fuel.

Driving down the raod you can push in on the clutch and it revs up fine. Let out on the clutch and it all but dies.

 

Usual problems are:

1) clogged cat. convtr

2) clogged fuel filter

3) vacuum leak (most likely on a 2.8L)

4) needs the carb rebuilt