i have a 04 d/a 3500 dually crew a month ago the rear seal blew out , the seal hasnt come in yet ,at the gmc dealer . the rear end has been running hot i checked the fliud, it was black and burnt and down a quart . i have never had a problem with the rear end like this . is the rear end damaged , will it last? or should i have the rear end replaced since its under warranty ?

It could have been set too tight. You should check backlash, preload and pattern.

Not to detract from the excellent advise of GMSID, but at least on the 2500's in 04 the rear end fluid level was changed from 4 quart to 3.littlebit. This could account for the quart low you report. When I changed mine at 500 miles it was pretty black also.

Jim