Acert help no power no fuel mileage

Nsx motor had it turned to 550 1850 still won't pull fuel mileage is horrible 4 mpg on a good day runs 1400 to 1500 at 70 to 73 shifts around 1400 to 1600 just babying it and still won't get mileage put a fuel temp wire on truck comes alive and mileage drops 3tenths or so. I'm at the end of the ropes with it either has to get some fuel mileage or it has to go. Truck is sick without the fuel temp wire tho it literally goes from hero to zero. Fan wants to stay on when without the fuel temp wire also. Any help would be greatly appreciated. It's flat top I realize it's not going to get the best fuel mileage this is pullin a reefer and a cattle trailer naturally mileage is worse with the cattle trailer. I really need to get 5mpg out of it to justify keeping the thing it's barely breaking even now. Thanks in advance

 

No it's gonna be in the tune I believe with the fuel temp wire on the fan doesn't ever really come unless with the a/c or a hard pull. When it's struggles without the file temp wire is when the fan wants to stay on.

 

Detroits and our other cats gettin 5 to 6 depending on drivers conditions etc. can't really run that speed either hauling cattle out of south Florida to the Texas pan handle on a time schedule.

 

Also have a neighbor with same set up flat top Trans and all avg 5 to 5.5 with cattle trailer.

 

And his pulled pretty decent as well