if looking at dumping my f450 and stepping up to either a 4500/5500 or possibly even 6500 with a dump bed. does anyone know what kind of mileagt to expect?
im dissapointed with the 8mpg im getting know and want to upgrade
also anyone know how difficult it would be to swap duramax into 90 suburban
thanks

Got a 4500, loaded to limit 8-9mpg unloaded bobtail up to 14mpg. Not a clue about swapping the DM, but bet it would be a pain considering all the computer stuff required now.

unloaded at 12k lbs on our 5500 4x4, all highway got 9mpg. Usually towing gets 8-9. Only did it a few times but fuel mileage is pretty crappy.

A Duramax can be physically installed nicely into a 90's Suburban. As other stated electical issues will be the main issue. When conversion is completed you will be an electrical genius. The Allison talks to the engine, the accelerator pedal talks to the system, etc, etc, etc. Typically need a complete parts truck for the swap. If you have to buy all the necessary parts/wireing etcetera your bank account will be severly depleted. The height of the Allison might require denting the doghouse, or raising the body. Complete wiring book for the 90 Suburban and the donor vehicle will be required (your bible). It is doable project but very labor intensive for the electrical issues.

Average between loaded and unloaded 8mpg. When loaded loaded to the max. All depends on your gear ratio and your unloaded and loaded weights with trucks of this size. They should all get between 8 and 12 mpg roughly.