'04 MP7 was an excelent engine. About the biggest issue was injector cups, and there's no update on them (like going to conicals) also, wirinharnesses were no where near life of chassis. Power wise, they were way more driveable than the last of the grey engines. Very good throttle responce and off idle torque. Remember, compared to the ASETs and AMIs.... a good running Briggs and Straton seemed powerfull. They aren't a powerhouse , like an old E7 427 or a Etech 460 would smoke them on a grade. Fuel wise, came down mostly to the right foot. At @ 73000/75000 pounds in the 6 to 6.25 MPG was realistic. I had 2, they both had a long life with minimal needs. I actually have a brand new one sitting here in my shop too. (yes, brand new Remack on the skid). All and all, by no means the worst engine choice I ever made.
If this is the same truck ???? just a couple things you mentioned don't sound right. Heavy spec aluminum frame ???? tri-drive ? I said it somewhat in jest about the pictures. (but God help us..... we love pictures) They really would be a great help for some input on this truck you're wondering about.
Sounds like a good time to take the oil pan off it, pressurize the cooling system and see where it seems to be coming from..... then get ready to spend some money.
Mark T's post in MP7 Engine was marked as the answer