I haven't tried it with our Mh but our 02 F350 tow vehicle I used a tuner sodl by the Dealer, and connected through the port under the dash. It had three stages. I only used the tow setting not either of the higher settings.The mileage increased very noticeably. Performance, without the Fifth Wheel was like a sports car.
Diesels now are turned down a lot. upping fuel and timing improves mpg and power.
too much fuel and timing can cause burnt or melted pistons but you're not going to run into that generally with a tuner. I can't think of the name right now but you can find thee or four, on the net. I would install a pryo monitor on the turbo also, just for info and in case a long pull uphill fully loaded, might raise temps bit too warm.
Cummins are stoutly constructed engines. Tuners aren't going to endanger their pocketbooks, generally, by selling too much tune.
I can't quote power increase or mileage increase expectations but I think twenty to thirty percent is reasonable in power.
Banks sells the Tuners too or did. The pipes and bigger coolers, and all that are too sell. Look on the Cummins forums on the net and make the decision yourself. I'm just saying what is available. I think the Tuenr was about four hundred dollars or less. They reset the tunen for me when the check engine lite came on when accelerating hard up a ramp towing.The torque converter clutch was unlocking( the weak link) behind the excellent 7.4 international Diesel and was nothing to worry about. In tat particular set up again I would adapt the later 6 speed trans and stouter torque converter behind the 7.4 diesel.
The larger intercoolers, radiators, and trans coolers, may not be required with a mild tune. Depends on how small your engine is now etc. The exhaust with cat and or the pig the pig p--- injectors( sorry can't think of the name) may be little different. See what the forums say unless someone come here with info where they have done it.