2000 w900, 4.5 mpg ???

How fast are you running when your at 6.1 mpg?

 

those numbers seem about right what were you expecting?

 

It's winter.....that alone makes a difference. FWIW, my truck gets around 5.5 in summer at 80k gross, running between 65 and 70. Over the winter, usually around 4.8. I'm. In the hills all the time though too.

 

Do you need high HP for any reason? I have the same year and same specks motor with 475 HP(factory setting) I get 6 Mile/ gal average pulling flatbed mostly heavy. Big HP not always good other than bragging rites.

 

Where did you find the 620 tune? Might be worth your while to do a different file, maybe a 550 brakesaver and a fuel temp resistor and see what happens.

 

I wouldn't expect that truck to do much over 6mpg under any circumstances. Might want to check you air to air cooler for leaks, though. That could be holding you back a few tenths.

 

I have a 00' W900L with an N14 set at 500 hp pulling a flat and step. Just got it this summer and have averaged 6.21 so far. I run 68 mph.

 

500 hp would be better for what he's pulling. He has too much motor unless he was pulling wide or heavy.