At work, we have a 2001 F-350 dualie deisel. and we are having issues with the thing because its becoming a bitch to maintain.we have to change the tires once every crop season but we have to replace the rear U-Joint every 3 months im thinking its because the thing is a dually, it gets mud stuck between the rear tires and throws the stupid thing off balance and shakes the whole rear end. this might cause the diff to shake just enough to wear out the U-Joint fast.
I was wonderin... is it the mud or is it the stupid truck that is a pain? does anyone else have these problems or have you ever heard of something of the sort?

If you are killing the u-joints that fast, I would check to see if the drive shaft itself is out of balance, or dented. An out of balance or out of round driveshaft can sometimes feel like an out of balance tire, and would definatly kill a u-joint very fast.

Many driveshafts come with weights on them from the factory, I would check to see if you can find any spot that looks like a weight has fallen off.

also, you can't always tell if the driveshaft is messed up just by looking at it. You might need to find a shop that could check it out.

Do you stop and go frequently, a combination of the driving environment that the truck is in and the mud can do that, or so says my uncle (he'* had a lot of heavy duty trucks)

How hard/soft is the truck driven? Mud can wreck havoc based on how wheels get stuck/spin back and forth so much..

meh its a work truck whats to hate. Not like its costing money out of your pocket right? Tell you the truth theres much worse out there.

Have you tried a sealed ujoint?

ok...We took the driveshaft out to get it checked at Pacific Truck parts. they said it was good. Its driven off road at all times. in mud and rough roads. and as far as how hard its driven... it was driven by a 65 year old foreman and it was just passed down to me friday. The previous driver, haveing age and experience, drove too slow, and me, lets just say i take advantage of the turbo . its not because i want to drive it like that, its just that the job needs to be done as soon as possible to get on with the next one to either work less or not work at all on sundays.

The truck is stock height but has a flatbed upgrade. we tow heavy farm equp with it too...just in case that matters.

Mud build-up shouldn't kill your U-joints. I'm in for something wrong with your driveshaft, or maybe a bad pinion angle.