We have a GVWC of 26,500, pulling with a '06 Chevy DWR. The thing about the mountains is not climbing, but coming back down safely. Rule of thumb, come down in whatever gear you went up in. Control your speed coming down but do so without burning up your brakes. I have pulled through the Canadian Rockies 3 times, up to Flagstaff, AZ (7.500 long pulling feet) 4 times and we are presently up in the Washington / Oregon area. The best investment I have made so far has been for a Banks Speedbrake for my '06 LBZ Duramax. It is like having cruise control for coming down hills and it works through the trucks computer by controlling the variable veins in the turbo. It is just like having an exhaust brake but without having to make any engine exhaust modifications. It works great and all I have to do is set the desired maximum speed and it does the rest without me having to touch the break pedal,,, AT ALL! This product is only available for the Duramax since, as far as I know, it is the only motor using variable pitch turbo veins but you can have a Exhaust Brake installed on the Dodge and Ford diesels.