Automatic problems

1994 T-100 4x4 with auto. I guess it is a 4-sp but it sure acts like a 5. Maybe a 4-sp with o/d? Anyhow, the problem is this. In o/d, the whole truck vibrates. It's almost like I lost a couple of cylinders and it runs REALLY rough. If I shift out of overdrive it drives fine. Doesn't matter if you're on the gas or off (not like a u-joint) it almost always does it. Seems to smooth out at 70+. Trans fluid needs changing; dark and smelly...truck was overheated by previous owner. Rebuilt heads, new H2O pump, head gaskets etc...love the rig but wish it didn't have this issue. Definately do NOT want to rebuild the trans. Think just changing the fluid will do it or is there a converter lockup issue or ?

It does sound like a problem with the L/U TC. Like maybe it's not unlocking when it should.
There is a solenoid that controls that.

I am having the same issue...been driving it with the OD not engaged . Any solution..? Same thing...don't want to pull the tranny..

I am having the same issue...been driving it with the OD not engaged . Any solution..? Same thing...don't want to pull the tranny..

How's yer transmission fluid looking? ;)

Need to change it but was wanting to know if anything else might be causing it...don't want to change it if it just has to be removed..

How many miles on it? Was the truck used to tow with? Does it slip or jerk in any other gear? Have you pulled the pan on it? Have you taken it to a trans shop?

Could be something as easy as a fluid change/purge.