1990 3500 4X4 Diesel with auto trans. The transmission has no reverse or high gear but will engage and pull itself in low and second gear. What all should be checked before the transmission is removed and rebuilt. Is there a chance of a simple repair?

 

It could be:
Low fluid
plugged filter
bad oil pump
VB with a problem,

But I suspect it is the front clutch pack, it might also be the rear band or clutch.

 

It there a port or a place to check pressure

 

1/8" NPT plug on the passenger side. About 1/2 way back.

 

What should the pressure be?

 

60 ish atidle, I don't have my FSM right here, but that number is close. If you pull the TV to the "back" of the tranny it should go to about 95.