I was just wondering on any kind of tips as to how to check and replace the motor mounts. My truck has 130,000 and was thinking this vibration could be caused by this. At first I was thinking u-joints but it didn't help one but. Its very noticable around 3000 rpms i'm guessing(no tach). In neutral you can rev it and still feel it by holding on to the 4x4 floor shifter. In gear you can smash the gas and watch the 4x4 floor shifter vibrate like crazy, and when you let off the gas it quits vibrating. So I guess I'm going to check the mounts to see if anything noticable.

 

Well if its an automatic you can open the hoodso you can watch the engine, have someone get in the car, keep their foot on the brake, drop it into Drive and power brake it a little, if the engine rocks a lot you can assume that the motor mount on the side that did not "lift" is broken. Then have them put it in reverse and do the same power brake thing, this will tell you if the other side motor mount is broken.
Get the picture?

 

If it looks like the shifter is buzzing (very high speed but light vibration), it may bode poorly for the transmission or transfer case.

 

If they are still making them like on the 92 model, you might notice some oil looking fluid around the mount that you suspect that is busted. (Thats only if you keep a really clean engine.) I noticed that on one of mine and thought I had sprung a leak. The mount had split in half and emptied its contents on the mount brackets and frame. In fact both mounts were bad, one had completely separated and the other was holding on by a small piece of rubber. Since I have the inline 6, changing was not too difficult as I was able to jack up the engine and change them one at a time.