I know I've read of motor mounts needing a couple drives to break in, maybe tranny mounts are the same?

 

Check your exhaust also.

 

If thats the case I have new motor and tranny mounts to break in. I'll take it for a spin tomorrow and see what happens.

 

Look here and see if your exhaust is "grounding out".

 

X2 check this. Mine was doing the same thing, it would vibrate while sitting still in drive but not in park. Although, I fixed it by replacing the trans mount.

 

My exhaust is so high after replacing my mounts that the cat hits the floor on a lip sometimes. I had a photo but I guess I deleted it.

 

The exhuast is clear of the crossmember. I drove it today and there's definitely still a vibration when accelerating 2000 rpm's is really bad. Its more noticeable now with the new mounts. It also vibrates more in reverse when standing still. In park its actually pretty smooth. There's no play in the t-case shaft or rear diff. The slip yoke has a bit of play up and down but I would imagine just by the ways it designed there would be some. I'm really not sure what else to check.

 

mine didn't hit the crossmember, it was too high and hit the floor.

 

I just removed the rear driveshaft and drove in 4wd. It was much smoother. Since I don't trust my original driveshaft I'm going to spring for new u-joints on the used one I picked up. If that doesnt work I guess it will be time to crack open the rear diff and have a look. I don't like where this is heading. I'll have to check the exhuast to see if its hitting the floor as well.

 

Im having a similiar issue. New catalytic converter and trans mount. Got vibrations pretty bad in drive at idle and at acceleration in reverse and drive. If it werent for the fact it does it at idle I would have suspected my rear ds.

 

I finally broke down and took it to a shop. The shop claims its a vibration in the transmission and wants to drop the pan to check it out. My only concern is that when i ran it with only the front shaft it was as smooth as silk. I explained this to the shop's owner and he tried to tell me that without the rear shaft connected it wasnt under enough load to cause the vibration. The truck was used to tow so I'm sure the tranny has had some abuse but I'm a bit skeptical about this diagnosis. What do you guys think?

 

I am also skeptical.

 

x3

 

Thanks guys, I'm going to take it elsewhere. Its hard to find an honest mechanic in my area.

 

Take your front shaft to a driveshaft shop.
Have them check for balance & install new u joints.
Reinstall then let us know.
I would re-examine or replace the rear u joints also.