Wow Ed, I'm very excited for you. What chassis is your truck on? Tag axle I thought meant a non-driving axle on the rear? Not very common on a truck conversion. Are you sure it's not tandem axle? Two drive axles? Tire pressure I didn't know you had to do them for individual corners on a diesel pusher. My truck mechanic said to run my tires at max sidewall pressure. My tires are rated at 110 psi cold. That means when the tires are cold you run them up to 110 lbs. This will make them handle better than a lesser pressure. Less sidewall flex cornering. It will also keep them from heating up as much as lesser pressure. When the sidewalls flex they generate more heat in the tire. They will also give you better mileage, a harder tire has less rolling resistance. Now, others will tell you a softer tire will be smoother and more comfortable. I'm fine with the ride on my truck at 110 psi. Others will tell you 110 is too much. If the manufacturer prints on the sidewall that the tires are good to 110 psi, then they are.
Basically, you can probably ask 10 different people what to run your tires at, and get 8 different opinions.
Are you picking up your truck at Renegade in Indiana? Take lots of pictures. I love pictures of truck conversions.
'03 Freightliner FL112, 295" wheel base, with '03 United Specialties 26' living quarters, single screw, Cat C12 430 h/p 1650 torque, Eaton 10speed , 3.42 rear axle ratio