hey so i was driving my truck today was getting on the on ramp and got up to about 50mph with OD off... and i felt this weird vibration then i push the bottom for overdrive and the rpm dropped and it was fine

and then if i floor it even in overdrive on the freeway and the rpms get close to 3000Rpms i have the weird vibration again

could it be a u joint starting to go out or ?

 

It could be anything. The fact is that you are exciting a natural mode with a frequency in the 3K ish rpms means its something rotating.

If its any of those components that you are guessing, then just get out and hand check for play in all of them. of course, park the vehicle.

 

Well put Wh1t3NuKle. Park it on level ground & leave it in neutral, crawl under it & grab the drive shaft & try to rotate it, then go side to side, up & down. If there is exsesive play, try wiggling it about again with your hands close to the u joints. It could be the tranny, but it seems a bit of a stretch. I have a 42RE in mine, when I take off it shakes violently - even stuff in the cup holders shakes right out! Turns out my 1st gear band & clutch pack are poop in mine. With what you described, I am inclined to think u joints.

 

Another test to try: Parked, brake set, engine running, transmission in neutral: Rev it up to your 3000 RPM that induces the symptom. If you get that same vibration, it's something between the transmission front pump and the radiator (but not including either of those).

 

yeah its not the motor i put it in neteul today and reved it up to 4k and its seems fine... once i get paid i'm gonna gonna repalce all the u joints... i haven't repalced them in a few years