Yeah, at first i thought it was the tires, but it is definately not coming from the tires. I can feel it in the 4x4 lever even though there is no front drive shaft hooked up, and no linkage going to the shifter yet. Could this possibly be U-Joint related?

Could very well be. Be a good idea to change them ASAP if that's what it is as there has been more than one trans. case destroyed here because of vibration from bad U-joints.

Thanks Arde,
I had pretty much decided to change them out as a first option anyway, but this just confirms my suspicions.

If you just put the tires on and the vibration just started, how can you be sure it is not the tires? Were wheels balanced? Check U joints as mentioned. Should not be any slack in them. And make sure they are fit into yokes correctly. Then reread the plenum sticky.

I checked the ujoints and they are great, new less than 500 miles ago, ot the tires because if i turn the overdrive off it goes away. I am at a loss, dont want to rebuild the tranny if that is not the issue.

Its most likely an engine miss.. When was the last tune up?

Who knows when the last tune up was, I just got it 3 weeks ago. I will ask the previous owner tomorrow at work, and if necessary, tune it up this weekend.