Hi Tom and Donna,
We don't have the 3400 but do have a 3670RL and pull it with a Chevy 3500. We wouldn't have anything else. We do lots of pulling up and down big hills and over mountains and the 3500 is a dream. The diesel mileage is always 10-12 pulling and closer to 18 just the truck on the freeways. The Duramax/Allison combo is a hands-down winner as far as we're concerned. So that's our 2 cents!
#29 fans Chuck and Linda Clements
Posey, CA
04 3670RL Big Sky
04 Chevy 3500 CC Dually 4WD Duramax/Allison