We own 2... a Chevy Silverado 3500 SRW (10’ Alaskan Camper) and Chevy Express 3500 DRW (Minnie Winnie 25B), both have 6L 324hp and GM/Allison 6spd tranny.
He’s my thoughts... having that SRW with 2,000 lb camper on it fulltime for last four years gave me a love of BOTH engine and tranny. Our 1st trip was 8,000 miles coast to coast and rtn with many side trips. Having ability to maintain engine at 1800-2200 rpm doing 65+ cruise is really nice. Going down a 5-6 mile 6% grade and having the tranny braking to hold rpm/spd is great. The cruise control is clickable... 1,2,3 up 1-2-3mph; 1,2,3, down 1-2-3mph.
6L Engine computer learns your driving habits and adjust fuel-power accordingly. When you replace air cleaner... always clean the Mass Airflow Sensor... disconnect chassis battery for 2-3 minutes. That resets computer to recalculate new air cleaner and MAS. It also re-learns next 10-12 trips of driver’s habits. That will increase your mpg.
Both my Chevy 3500s have a haul/load mode switch to tell computer when you’re running heavy or pulling a load. Remember trucks are designed to run MT and fully loaded. Both our 3500s run heavy at all times, as camper has never been removed and our Class C Minnie Winnie is a constant load on that 3500 chassis.
After 4 years with that 2K lb camper set-up on 3500, we saw our new Winnebago 26’ Class C with that same GM engine-tranny and went to look at it... While service mgr and I are bent over looking at DRW disc brakes and suspension... we hear my lovely wife telling the salesman “I think we’ll buy it...” We did...