Rear end problems...

So I did a gear swap around 1000 miles or so, and now I am hearing a hum/vibration coming from the rear end. When your driving the hum/vibration gets louder as you increase speed. Now everything was fine after the gear swap no whine or vibe. When you put the truck in N when your at speed the problem is still there, so to me that rules out u-joints. I have looks at they u-joints and they seem fine. I have also looked at the wheel bearings and they seem to be good. So I am wondering if something is wrong with the spider gears or one of the bearings inside the diff. Has anyone had any experience with issues like this?

 

A 1000 miles is not fine. Improper install can last that long. Assuming there were no issues in the axle area then it has to be one of several things in the pig.

Improper carrier bearing preload.
Improper pinion preload.
Improper gear depth.
improper backlash.

Each item has it's own quirky noise.

Give it a good ride;

sway the truck going straight
on and off the gas in third gear
sweeping turn left and right.

sway the truck in neut.

Please do this safely.

come on back and I'll try to get you in the right direction.

I also need to know all the parts you replaced. be specific