Best Choice for Gas Mileage?

I am considering a new silverado either the 1500/2500 ext cab or crew cab. If given a choice of the 4.8, 5.3, or the 6.0; which gets best bang for the buck. Without getting technical, I had the local chevy dealer redial the prom in the computer to get better mid-range power. The truck I have now, a 2001 ext cab 1500 with 3.73's, has a 4.8 in a on P245/75-16 m+s Michelin LXT's and getting 16.8 city and 19.6 hwy.
Has anyone seen better figures with the 5.3 or 6.0 engines. I know if I go with the 6.0, I'll need to get into a 2004 3/4 ton model, as they apparently stopped building the 1500HD which came with the 6.0 engine. Anyone with any experiences that does mind sharing would be welcome.

i got the 2004 Silverado 3/4 model 2500 (non-HD) Crew Cab 4x4.. ~~cough cough~~ Harsh Ride, 15mpg tops on highway mileage. other than that.. it's great =)

My buddy has the 5.3L and I have a 4.8. I am defintely getting better gas mileage then he is, and the performance difference really is hardly noticeable (his is stock and mine has an intake). At first I was upset that I didn't get the 5.3, but now I'm happy I ended up with the 4.8. For a truck getting 17mpg driving in Miami traffic jams what more can you ask?!! :biggrin: