I have 2000 silverado with 6" fabtec lift and 35's with 3.73
my rear differential just blew up. 175000 miles on it.I want to regear with4.88 but don't have cash to do front and back now.Can I do the back now as long as I leave the truck in 2wd would that damage anything if I drive it?  

YOU MIGHT BE ABLE TO MAKE IT 2WD BY TAKING THE FRT AXLE SHAFTS OUT BY UNBOLTING THE SHAFTS FROM SHORT SHAFTS AT THE PUMPKIN AND SLIDING THE SHAFT OUT THE INSIDE OF THE HUB AND TAKE THE FRT DRIVE SHAFT OFF TOO...THE HUBS SHOULD HAVE NO PROBLEM W/NO HALF SHAFT IN IT...ANY THOUGHTS ON THAT!?  

BUT ONLY AS AN EMERGENCY FIX  

This is not surprise. The "G" in the G80 stands for grenade when you lift it and put big tires on a 10 bolt. (It is not a posi that will take much abuse with big tires) I am surprised that tranny did not blow first with 3.73's and 35's though. Now is the time to hunt up a 14 bolt 9.5 semi floater for rear. It can be had in 6 lug flavor and is a LOT stronger than a 10 bolt and even a G80 in it does much better too. (the extra inch diameter in carrier posi unit does wonders)  

I agree with snowman, upgrade that axle.  my friend had the 14bolt hes talking about in his z71 in the 6lug pattern and it never complain of the rock and mud abuse it went through with 37s and 4.56s