Well, my Avalanche came with a bed mat, and it left with no bed mat! The Avalanche bed mat fits perfectly (width) in the Rambox bed, except its 4 inches shorter than the Rambox bed. Perhaps this is why the dealer needs my truck back in to install the trailer brake controller, to flash the computer as you indicated? It goes in Monday for this installation, Tonneau cover install, and window tinting!
A few things I've noticed, the engineers made this thing to shut off cylinders as soon as it can, and the fuel cut-off on deceleration is silent, but, I notice it. As you coast to a stop, the 6 spd tranny engages 1st gear, the ECO mode shuts off and all 8 Hemi cylinders are firing. I have noticed avg about 14 mpg, but, I only have 259 miles on the truck so far! On my first and 3rd day owning it, I have had to use the bed to haul parts around in for work, so, this is how its supposed to be!