Another fact: almost any engine modification which increases power - that includes chips & programs today - will also increase fuel consumption.
One thing that is a win-win proposition is synthetic oil in the transmission and rear axle. It reduces friction, lowers the temperature and is more tolerant of high temperatures. This is not to suggest that the rest of the transmission will tolerate high temperatures just because it's filled with synthetic ATF - the clutches, seals, o-rings, solenoid winding insulation and a myriad of other parts remain vulnerable to the heat.
Synthetic oil in the engine will provide the same performance benefits, but it's probably a money-losing proposition with the short oil-change intervals necessary. Synthetic oil doesn't extend the oil-change interval because it's driven more by contamination than oil breakdown.
Low-pressure-drop intake & exhaust modifications boost the maximum available power by reducing backpressure losses. They won't be nearly as effective at increasing fuel economy. Because the intake & exhaust flow rate while cruising is much less then it is at pedal-to-the-metal, the pressure drop of stock intakes & exhausts is also much less.
The single biggest factor affecting fuel economy is driver discipline. Large fleets routinely see a 40% difference in fuel use between their worst driver and their best. Use your cruise control, factor in the wind and keep meticulous records. If this engine has an OBD-II port, (I don't remember which year that was implemented) get yourself a data display device and read up on "hypermiling
) Even a 10 or 20% savings will make a big difference in your bottom line when you're burning 300-500 gallons per week. It may sound counter-intuitive, but you can often make more profit by driving fewer miles.
The next thing I notice about a wedge carhauler trailer is the aerodynamic nightmare. I suspect an aerodynamic makeover could reduce fuel consumption by at least 20%. An air deflector on the roof of the truck, a bulbous nose on the trailer, paneling over the trusswork underneath, fairings over the wheels, loading the shortest car first, facing aft, and stretching a tarp(s) over the cars after they're tied down. With a little extra work, you could install a sleeping berth amidst the paneled-in trusswork underneath, like a Japanese capsule hotel. No room to stand up, but plenty of length to stretch out.
If you're just getting into the business, I'd suggest initially laying out the minimum amount of cash possible until you get a feel for things. Several months on the road and reviewing your books will tell you what you need way better than any amount of Internet advice.
Ultimately, you need to make the decision whether you're going to be a truck & engine enthusiast or a businessman. Chrome & stainless steel may fulfill the ego but they empty the wallet.