I did a visual check of the u-joints
There is a very effective way to check the u-joints on your truck to see if they are failing. Either the u-joint will feel sloppy because half of the needle bearings have fallen out, or the u-joint will feel tight (as it does normally) because the bearings have seized and have not fallen out.
Since you say that u-joints all feel normal, I am suspecting that one or more posts are seizing, so try this:
After the truck has been parked for several hours, take it for a short test drive. You don't have to go very far, nor do you have to get it up to highway speed. The purpose for the short test drive is that if a u-joint bearing is seizing, it will build heat rapidly and will not have a chance to conduct its heat to the surrounding drive train before you inspect the u-joint.
Immediately after the test drive inspect each post of each u-joint by using your fingers (carefully, as it may be very hot) to compare temperatures. Since you have a three u-joint driveshaft, you will be checking twelve posts. A normally operating u-joint post temperature for this test drive would cold to lukewarm. A seized one will be very hot. Be sure to do your inspection right away, as the longer the truck sets, the heat will spread to surrounding components, thus muddling the test results.
If there is no slop in all the u-joints and there is no temperature buildup during the test drive, then you should look elsewhere for the problem.
- John