took the truck in to get axle seals done then there sayin that the actual locker portion of the diff is buggered so i gotta get a new one, anyone able to tell me what diff i have in my truck ?

2003 gmc sierra 1500hd 6.0

 

should be a full float 14 bolt

 

Most HD1500 that I remember had semi-float 14 bolt rear axles.

 

To the OP, post up your G-codes from your glove box. Or call the dealer with your VIN and get them. That will tell us which diff you have, the ring gear size and ratio, etc.