Financing a Truck and My Experience

[Longshot]

Thanks all for the inputs and I agree 100% that not all drivers should be owners and with most of the opinions and advice from all members mentioned here.
All of what Rawze stated about operating efficiency is true of my family member's methods like driving too fast and paying for repairs that could have easily been done with a couple tools in 15 minutes. Case in point; truck would not regen so I found on this forum information about diesel doser, so I went out to the truck unbolted the doser, totally caked over, would never regen, so I cleaned it up in about 15 minutes and it regens fine now, no issues. Family member said "wow, I paid $1000 to have that doser replaced on one of my trucks".
I found a Cummins document about how to get the best gas mileage and it covered most of what everyone has stated here and for sure most of those best practices were not being followed by my relative and I have mandated that going forward speed will be monitored and must be maintained at Cummins best practices guide - in top gear driven at whatever road speed equals 1400 RPM and preferably 1300 RPM but not more than 62 MPG as a normal practice.
I will monitor with a combination of Bluefire engine data collection and GPS data from Traccar which I have setup on my own server at Amazon.
Just to be clear, I did not buy a truck and turn it over to my family member, I will basically fulfill owner functions and he will drive and either meet my guidelines or I will put someone else in the rig who will.
We will follow a rigid maintenance regimen that includes routine replacement of parts at manufacturer recommended intervals. Thoughts on that one? What would you'all think of replacing NOX sensors at 200K miles for example?
All revenues come to my LLC bank account and I will hold out for repairs, maintenance, and investments like low rolling resistance tires, low flow air filter, bypass oil filter and maybe a Bully Dog unless this group thinks there is a more cost effective solution - Rawze mentioned Pyro Boost Gauges ?. Is that a good alternative? Sounds like it? Thoughts?