Gypsyman,

I realize that I'm over the GVW. The truck runs fine on flat ground even mild-medium hills. But the Mountains were different.....

 

My first truck was an 03 3500 duallie 48re automatic 2x4, and I pulled a 37' triple slide 5th wheel RV Trailer (heavy 16k+). I was really pleased with it. I was looking forward to traveling out west several times a year, which would include the Rockies and Sierra's. I took it on a test run to Smoky Mtn National Park accross US 441, over New Found Gap. Gatlinburg to Cherokee. I found the transmission and braking to be inadequate. Tranny got hot and slipped. And alot of extended braking on long downhill grades. I figured up the cost to modify the tranny with VB/Torque Converter, and other improvements I wanted and decided I would be better off cost-wise to trade it in. If you were to just pull your own RV occassionally, a modified Auto might be fine. But I go to California many times a year over Tehachapi Pass, Grapevine, Donner passes, Vail and many others. I recommend a 6 speed and Exhaust brake for peace of mind and endurance. 4x4 comes in real handy too. The truck I have now is far superior for towing than what I had before. I pull heavy RV trailers requireing a CDL, and would not go back to an automatic. This is just my experience and opinion. I've pulled 60k+ miles this last year, and I'm pretty sure the auto would have bit the dust even with mods. Not to mention the Braking issue. I take it easy on down-grades and still I've smoked a few quit a few brakes. I installed a PacBrake and quit worrying about brake fade and failures.

 

It's a Weekend Warrior (pic in gallery) with a 13,000 lbs GVWR. We had it loaded plus the pickup bed was full and 5 people in the cab. My buddy has an 03' Duramax with AFE, Banks exhaust, and Edge w/ Attitude set on level 1. He weighed in about 2,000 lbs more than me and we ran neck and neck with each other up every hill for 2,000 miles. My other friend with a 7.3 and Banks chip towing 20K fell miles back on some of the long passes in Oregon.

 

I think the point is that somthing may be wrong with the truck.

 

start with the simple stuff. new air/fuel filter
then find the nearest cummins shop with a dyno and pay the shop to test your truck. When they tested my '93 they hooked up the wires and hoses got the boost, what temp the fan came on, hp and tq at what rpm.
This will take the guess work out of "is my truck running right?" If your engine is within spec you know you need to do some modifications, if your engine isn't within spec, you know you need to get it fixed before you can even consider doing any upgrades.

An example of a problem would be a dribbly injector. You may not be running right on all 6 cyl....