I'll cut straight to the problem. I have a 97, with the 3.4 V6 156,000 miles, 4 inch lift, 33x12.5x15. I have run into a vibration problem. I just put on new rubber, less aggressive than my previous tires, but the vibration continues. It occurs between 15-30 mph, then magically dissapears once it gets past the 30mph mark. I thought it might be the clutch or pressure plate but it still vibrates when I disengage clutch. My alighnment and front end seem fine, no vibation through the steering wheel. I'm beginning to think it might be the driveshaft bearing or something in that area. I was wondering if anyone out there has run into the same problem and if so what advice they have to fix it. Thank you for any help.

Maybe stearing rack bushings?Possibly inner/outer tierod ends?

All yer lugnuts tight and torqued? Mud on your drive shaft or your wheels?

If it's an extra cab it could be the center support bearing on the drive shaft going out.

What is the frequency of the vibration? Wheel speed? Engine speed (probably not if it continues to vibrate with the clutch disengaged)? Driveshaft speed (about 4x wheel speed)?

Knowing the frequency might give us all a better clue as to what component(s) we can rule out/in. Good luck!

Thanks for all the help. Just a little update....I checked my driveshaft and found that there was way too much play when I shook it back and forth. I found that the u-joint was in sad shape with the bearings starting to blow out. I replaced that and the vibration is almost gone. I have a feeling like solidblk85 suggests it may be the support bearing, in fact I was just talking to one of the buds about borrowing his garage so I could change it. I will be replacing it in the next couple weeks and I suspect all vibration will be gone. I keep you posted.