1990 Fullsize jimmy low speed vibration.

I just bought a 1990 Jimmy and I don't know to much about it yet only that it needs some work. I noticed that its got a low speed vibration from about 5 mph to around 15 to 20 mph. It got a 6'' lift on it and looks like they replaced the driveline and also it makes a clunking noise when I deaccelerate and accelerate. Do you think the vibration could be an unbalanced driveline and the clunking a bad u-joint. Any help would be great.

does the truck have aggressive tires on it? and do you know if it was heavily used in the woods? reason i ask is because when i installed a loc-rite or really any spidergear replacement locker there is a clunk upon heavy acceleration and pretty much all deceleration if you let your foot off of the pedal completely. probably not the issue but you said it was lifted, it could be something like this.

more likely the clunking is a bad u-joint but you should in theory hear the clunk everytime you put the truck in reverse or drive (automatic). you could test this by parking on even ground and putting the truck in Neutral (chock the wheels just in case) and get under the truck and start shaking the driveshafts around. any movment at all dictates bad parts. If you can move either side of the driveshaft at a union then the u-joint is bad. if you can move the slipyoke at the back of the trasfercase you could have an ovalized yoke or the spline could losening up.

rule out the simple stuff first start with the driveshafts and move outward.
List of possiblilties:
- u-joint(s)
- bad yoke
- bad pinion bearing (rear)
- hubs are still locked (bad front d-shaft angles)
- lunchbox locker (have slop to work correctly)
- axlewrap (very slim chance)
- bad shock bushings somewhere

Thank you very much for the reply. I will check it out as soon as I get it back.

you're quite welcome hope this can end up helping you out