I forgot to include that I get about 17.5 -18 mpg in town and 20 on the interstate. Premium fuel makes no noticable gain,but opening up the exhaust with a glass pack ( no cat)helped greatly compared to stock exhaust.Header didnt seem to do too much ,but I needed a new ex manifold anyway.

Is it a 5-spd or auto, if auto that mpg is about right.

Have you looked at the beaks, you could have a sticking caliper or rear shoe that is causing a drag on the drivetrain.

You could also be running rich, and simply wasting fuel. Check for vaccum and exhaust leaks. You might also want to check/adjust the valves, a loose one will hurt power/performance.

What is the age/condition of the spark plugs/wires, and the cap & rotor, it might be time to replace those as well.

My auto 22re gets 20 in the city with some highway and 23 or a little better all highway this time of year with temps in the 60's to 80's. In the coldest part of winter here, 10 to 20 degrees, I was getting 17 or 18 in the city, and 19 or maybe 20 on the highway. The mileage I am getting now is just after a new timing chain, and head cleanout, new valve seals, etc. I also have all my emissions equipment installed.
I still say there is no reason to poison the air, even if you decide to eat an owl or two, while dreaming about running a two stroke motor in your next truck. Just think of all those children suffering from athsma, while chopping down the tallest redwood you can find, and consider using a catalytic converter. thanks

Put a new cat on it. It's cheap and it cuts down on emissions. Why lighten up for calling out the fact that you've not only committed a federal offense, but you're doing nothing to help your economy? You can get a cheap high-flow cat from any parts store and breath better.