best RPM

can anyone tell me what the sweet spot is for my 2005 Chevy 3500, Duramax engine, 4X4 Dually Crew Cab, long bed with auto trans and 3.73 gears. I know the sweet spot to run my 2003 Harley is 53 mph for the best fuel economy and all around performance, not saying I run her there but that is the best spot for the bike if'n I want to get the best mileage for my $. I was just wondering if anyone new where the best spot for my truck is in regular mode and also in tow/haul mode, there must be a certain RPM for the best fuel economy empty and towing my 9000# TT. If anyone has this info I would appreciate if they were to pass it on to me so I can be a educated consumer. Thanks

Not sure with that truck really, but most GM trucks get best MPG around 1400 rpm or so. Normally, ~60mpg in high gear.

oops, that's a diesel, ignore my post then lol