I was looking for some input on a vibration I noticed. Here are the symptoms:

Slight vibration at idle, a little worse at 800-900 rpm(while warming up) not as noticeable once warm around 650 rpm. The more worrisome one starts at around 2700 rpm. It is noticeable in all gears, under some throttle during acceleration and at constant throttle. I first noticed it when I turned overdrive off going over the pass, and was cruising at about 3k. I don't get the truck fast enough in overdrive to find out if the vibration is there. It is also present in neutral when I Rev it, but harder to notice with no load on the motor. I have checked front and rear u joints and think they are in good shape, but am working on getting them replaced anyways as a member here suggested but I don't think they are the cause. I have the full time 4wd version if that makes a difference. I am not sure, but I don't think the two vibrations I described are related. It runs very smoothly between these rpm ranges and at normal cruising speed. Any input would be appreciated

 

I would try removing the fan belt and see if the vibration is gone. This is to make sure the vibration isn't belt driven.

 

How long is it safe to run it without the belt? Is it drivable or just to test in neutral?