I have a 1984 Chevy P30 step van and run it for my coffee truck. I just recently changed the alternator and then out of nowhere it stopped shifting gears and going at normal speeds easily. I have some people saying it's the transmission and now the carburetor. I'm not sure if I should attempt cleaning the carburetor myself or take it to get the transmission replaced.
You didn't say which engine and transmission it has but it's a 1984 GM so it could be just a bad vacuum modulator. If the diaphragm breaks it will suck transmission fluid up into the intake through its vacuum line creating multiple driveability issues.
It's held onto the transmission by a retaining bracket and 1 bolt.
This is a really good point. The transmission fluid is running out fast I'm having to refill it now monthly. I'll ask my mechanic about it being this.
How long has it been since the transmission was serviced? Does it have enough fluid? What does the fluid look like? (Burnt? Gritty?)
I am unsure when it was last serviced but I've checked the fluid plenty of times, it's running out pretty often now. It looks normal when I take it out but now I'm thinking it might be a leak.
Certainly if it's running out of fluid it's leaking. Not unexpected in a nearly 40-year-old transmission. However, check the vacuum modulator if equipped with one as @jack62 recommended.
What is the service history of the transmission?
