Yo Hoot,
Well, the only thing I can tell you is that these trucks equipped with the 48RE transmission have had failures as early as 15,000 miles. Seems DC didn't engineer the thrust washers to the right specs and they fail prematurely. Even on a stock vehicle you are taking a risk. There are several transmission companies out there that can upgrade your transmission to help you from having failures. I took my 01 truck with a 47RE and had it upgraded at 12,000 miles. I figured that with the weight I hauled that a "better safe than sorry" approach was better. DTT did my upgrade and the truck now has almost 100 K on it and is running strong with 450 HP. After you do the transmission I would put on a turbo of your choice and an EZ with stage 2 injectors (80 hp) and never worry again. With the 5 inch exhaust you have and a bigger turbo you will be able to haul anything at any speed and never worry about EGT's. Plus having an upgraded transmission, you'll finally put the HP to the rear wheels.....
Greg