just got a 1989 snow plow 7.4 3500 and it starts and idols but dies under load only when in gear ...it revs up great. Do the map sensors get stuck on these...looking for some advise how to trace down the problem without going down too many rabbit holes. thanks

 

possible solutions first are
1) change fuel filter
2) check all vaccum lines. (seem ok on visual)
3) change fuel pump and sending unit...and inspect fuel lines..
4) map sensor?
5) egr?
6) change o2sensor and check cats...

 

it was the map sensor.....I just unplugged it and plugged the vacuum line and it runs like a champ!