I just got a 1991 f250 diesel 2wd. It has the e40d transmission in it. It has only 91000 original miles on it.
Well when I went and got it, it drove good for about 80 miles then I was cruising at like 70 on the interstate and all of the sudden the Rpms went up and the speed went down. The gear didn't catch again until about 50mph.

Now SOMETIMES when we get in I get hard shifts and it acts like it doesn't want to shift or wants to go back and forth. But then sometimes it's really smooth shifting. It had started doing that so we changed the trans fluid and there was no big metal flakes in the pan or anything like that. Added the oil back and added Lucas anti slip stuff.
But it still does it only sometimes.
Off of those details can anyone tell if the trans is bad or if it may be the solenoid pack inside the trans that is going bad. Or am I way off?
I also went and talked to a transmission shop and they actually said it sounded more like the TPS than anything else.
Any help would be appreciated

 

is the check engine light on, or is the overdrive light flashing? that will tell you if there is a trans code or not. without a trouble code there is only guesses to be made as to what the problem is.