2500, 155", 157K

Has the 2 piece driveshaft

From the look of the cover, it looks like a 9.5/14 bolt.

As I said, I don't know jack about differentials. However, I think what you are talking about only exists on some 99-2000 express with 10.5/14 bolt. I could obviously be completely wrong.

 

9.5" semi-float 14bolt would require full disassembly for pinion bearing replacement, I think your mechanic is short on labor. If you have 17yrs and 157k miles on original u-joints and center driveshaft carrier you got all the moneys worth from them..

 

Without being an expert, the only sure way to ID the diff is to have a dealer decode the VIN. A simple decoder like the one in the tool bar (above) doesn't give enough detail.