I did that on my first diesel pick up. By the way, we don't use the term "GAS" here unless you are referring to a GAS VEHICLE. It causes too much confusion. Try to use terms like "throttle" to save confusion. :)
I had an air compressor that I mounted under the hood of my 2004 6.0 for air horns. I had to make a bracket to mount it to the left side inner fender. I had a tank I mounter under the truck for the reservoir and an electric valve to "honk" the horns. I got my stuff at...
You will need a good scanner to read the trouble codes. I have an Autoenginuity software/hardware package that loads onto a Windows Computer to read the DTC's (Diagnostic Trouble Codes). Thee are a lot of small hardware scanners you can look at. Just make sure they will read our trucks codes...
Are you running the correct tire pressure for the weight of the truck and load? It does sound funny to be wearing the inside (Tread?) or both rear tires.
It will sag without you in it. You have used the springs on that side more than the other side and it shows whether you are in it or not. They are sagging more on the drivers side than the other side.
Measure to the body and you will find the drivers side is lower. I have seen this on my 2004 F-350. You are always in the drivers seat and not always some one in the passenger seat.
I have a friend who has a 2000 F-350 Dually. His hubs are the same as mine (2004 F-350 not dually). There is an adapter for the ten hole wheels but nothing for the hubs.
Red Head Steering Gear has nice rebuilds; http://www.dieselpowerproducts.com/m-183-red-head-steering-gears-inc.aspx They are not the cheapest but it is YOUR life here. Check them out.