When accelerating, my truck has always shuddered between 5-10 mph, then when it shifts into second it always hits really hard. The check engine light has been on as long as I've owned it, and it has had a stumble at idle.

I haven't had a whole lot of time to check on any of these things, but today I finally got off my lazy butt and checked the transmission fluid. A little low, not bad. Took a half quart to top off. I then sprayed off my truck, exterior, undercarriage, and under the hood. Took it for a drive and the idle started shooting up to about 2 grand and there was nothing I could do about it. And it wouldn't shift out past second gear. Drove til I could pull over safely and shut it off. Started it back up and it was amazing. The idle was smooth, as could be, the check engine light was off and it is shifting amazingly smooth and the acceleration shaking is gone completely.

Hey, I'm not complaining. None of the problems have returned, either. I'm just really confused as to why so many problems were solved with a half quart of transmission fluid and a engine spray down... 5.8 auto trans. What do you think?

 

Still running great, the only thing I noticed now is that I need to time it.. It's running like a like a completely different truck. I can't even feel its shifts now.

 

Good to hear that the truck is running better but I see no mention of you pulling the codes? This is the first thing you need to do to begin to diagnose the problems you are having and may continue to have since you have repaired nothing so there's no reason to think the problems won't come back. The engine spray down may have temporarally improved contact between two devices or shorted something out causing the computer to go into open loop. That may give the impression of improved operation but you may have actually caused more damage, so you need to talk to the computer to see what it knows about the condition of the engine, codes are stored in memory and the fact that the check engine light went out means nothing, the problem that caused the codes can still be present.