Low boost and poor MPG

[86chevy]

:D :confused: I have a 1996 suburban 6.5 that I have had about 3 months. It has a remanufactured engine with 3000 miles, and a remanufactured turbo, turbo-master turbo control, 3.5" exaust, heath deisel power PCM, intercooler, new lift pump with 7 psi, relocated PDM, gets 11 miles to the gallon (not towing and on the highway), and only 6 pounds of boost. I have adjusted the turbo-master,tightening it all the way down to where the sping is only about 1" and still only build 9.8 pounds of boost.There is no black smoke. The timing offset is 1.94. Which direction should I be looking, any advice would be helpful.

Doug
1996 GMC Suburban 6.5

[Hubert]

1st easiest thing would be get a little stiffer spring. It might have fatigued or other??? How are you getting ~ 10 psi accelerating? How much go pedal does it take to cruise say 60 mph and what rpm are you running then? What size tires and gear too? I use very little pedal on flat highway and about 1700 rpm in 5th gear - 265/75R16 3.73 gear. MPG is really affected by rpm, air speed (and other rolling resistance), and pedal position.

Completely new rebuilt engine? IP-injectors age? Miles on vehicle/transmission?