CM870 economy

[BradyHodges81]

First time post: Recently got a 2006 truck with this engine. EGR is intact and after watching your video on an 871, I cleaned as many sensors as I could get to. Before cleaning I got 4.1 hauling an overweight load 1000 miles, got 6.5 bobtail coming back. Only mod, put a 6” single stack in place of the muffler. Also... this is a 450 engine, the person I purchased from said a 550 cam had been installed. I’m not sure if tuning was performed or not. It feels a little weak to me. Question time... is that normal mpg for this engine? Is there tuning I need to have done to maximize efficiency (if so, who;how)? And finally, what do you recommend for upgrades to this engine to gain a couple more lbs of power but mostly for economy?