Just picked up an 03 Silverado with 4.3. Will be changing the v6 for either a 4.8 or 5.3. Planning on a single turbo, hoping to get it into the 800s and also have it as a cruiser. I’m wanting a boosted 4.8 but part of me keeps saying 5.3. Can someone give me some insight on which one and why?

 

stock gen3 4.8 will hold 800 longer than a stock gen3 5.3 because the rod ratio is shorter and the pistons have less leverage on the rod

5.3 will make more torque, will spool the turbo faster and will drive better when out of boost. will also drive better thru an auto

For a truck I'd pick the 5.3. For something with a little less weight and you have a manual and can take advantage of the higher RPM.... 4.8

 

Might as well put a lq4/9 in it if you're going to swap it.