My 88 3500 with the turbo 400 has an intermitten shifting problem.Most of the time it acts like it is stuck in the passing gear mode. I thought by unplugging the wire that the denten switch wouldn't activate but it did not help. Is there more than 1 wire that plugs into the tranny? So far I only found one.

 

should be all controlled by the detent and throttle cables, old school on that one.

 

It doesnt use a cable, there is a electcical switch on the carb that activates a dentent solenoid in the tranny. I have only found one wire that was plugged into the trans. I would like to disable that soleniod. Now when I drive it it'll stay in 1st until I get to about 35, barks the dually,s then won,t hit 3rd until around 50mph. Sometimes it will shift fine in the morning until I shut it off. Then it goes back to the same ol' crap.

 

all thats controlled by that is tcc lock up...doesn't it have a modulator?

 

sounds like your motor aint runnin to the fullest, i was having almost the exact problem a month ago, it wouldnt shift out of first till about 35, second at about 45 and then about normal. got the motor running a little better shifts great and on time now. id say a good way to check this out and see if its the motor or the tranny, gas it alot more then usual under normal driving and see if its shifts at the right speeds.

 

It does have a new vac modulator but no lock up converter. The motor runs very good.

 

After reading thru some manuals, I have determined that it must be a high pressure problem.I guess the vac mod controls pressure, but it is new. Maybe the valve that it controls is stuck.