What should I look for in a new truck?

Sounds like something is wrong with your engine from what you described. 435hp is not a lot, but is plenty.
Had a 425hp 3406B back in the days. If I catch up with someone I’ll pass them without a problem.

 

To achieve that you probably need faster rear ends and more motor.

I'd buy a small coffin sleeper, 550+ horse 1850+ torque, 3.08 rear ends. Maybe even 2.79 or 2.64 if mostly always on flat land, but 3.08 should cut it. Ideally if you have a good 6nz or 3406 cat you can build it a bit (injectors and turbo) and tune it so you can run 800 horse and probably 2400 torque. With 3.08 that thing will be a beast. If you must maintain your driving habits and forget about fuel economy, that is. I prefer an 18 speed but a 13 would probably be just fine as well. If you decide to go to very fast rear ends, below 3.08, get the 18 speed. You need the double overdrive final. If you get a 10 speed direct final even with 2.64 your rpm will be high at like 70 mph leaving you not much left when you need that 75-80 which is what I suspect is happening now.

 

1st off I dont see any reason to run 75+mph when loaded up.

But what trans do you have? What rpm's are you at when in top gear at say 70mph?

If you bought the truck used, there's no telling if its been electronically limited. Its possible to limit rpm and power in every gear.

 

Btw a 379 with a C13 is a heck of a truck, not much better out there. There's so many things you can do to that truck to fine tune it to what you want.

 

I think he's part of a crew and pays them by the hour
So every 1 hour more on the road costs him a lot more than the fuel saved
The crew travels as a convoy, I think

 

The rear end gear ratio is the problem, he's geared for speed not pulling.

 

You should be able to get a decent tuner to put on that to help the power a little bit, I'd find a good independent truck repair shop that knows more about them though.

 

Your truck sounds like it is down on power, when were the fuel filters changed? Do you have a DPF? 07 build shouldn't but, exhaust restriction? Get the ECM set to 500/1750 What RPM are you at when the truck is on the hills loosing power?

Steve