Hi guys new to the forum here, this is my first post it looks like you guys know your stuff so here it goes. I have a 2001 express 3500 with 4.10 gears no limited slip/posi and I was looking to change to maybe 3.73 gears with a posi for better mileage/traction I was looking for years that interchange. looking into swaping to the newer rearend with the disc brakes if possible/cost efficient. The other option I was thinking is a powertrax "locker" wondering if anyone has any first hand experience with these units

 

I have the g80 locking diff with 373 gears on my 2002. I get 13 mpg city and maybe 15 hwy. Not going to make much of a mileage diff for the cost.....however the locker is great but prone to failure since the internal parts are so small. Mine broke, and now its a one tire fire.....sucks.
You could switch axles or have your rebuilt.....

 

will a pickup rearend fit? are they the same? and 13 mpg would be great in town, currently getting 10

 

I think they are. Gm uses same parts across several platforms.
Just double check the length and so on.