Ism cummins 410 hp with emissions

[maddsports]

I am trying to get this ism cummins to be a fuel efficient truck it currently getting 5.5 mpg and. I would like to get upper 7 plus it had a high crankcase pressure code and a leaking exhaust o am planning to do a egr tuneup to see if the mpg can improve. Also I was to figure out the best sweet spot to govern it so it gets the best mpg ratio is 3.78 or 4.11 so far I think 65 is the best but over 65 mph the rpm is 15.50 of higher