As previously stated, most of the items mentioned are for gaining HP, which is typically counter productive for fuel economy, although if you drive like a little old lady, you might see a small gain in MPG. The cost of most of that equipment will require many years to payback and you may never fully recover their costs.
As a comparison, I used to get just over 22 MPG on the highway with the only modification being a drop-in K&N filter. That was acheived by driving between 70-75 MPH and about 500 lbs of luggage and gear in the bed and under the tonneau cover.
The best and cheapest thing you can do to get better mileage is to insure the truck is properly tuned: You are not carrying excessive, unnecessary weight; and that your driving habits are designed to save gas. Any acceleration eats gas, so you need to accelerate more slowly, and don't change speeds even on the highway. If you are driving faster than the majority of the vehicles on the highway, you will constantly have to slow down and speed up.
I found that if you go 1-2 MPH slower than the rest of the traffic, you wil lsee a very noticable improvement in your gas mileage. Not solely because you are driving slowere, but because you will not have to slow down for slower traffic and then accelerate back up to speed again.
I have gotten my best mileage on the highway by driving late at night after midnight, when there is little or no traffic on the road. I have driven nearly an entire tank of gas on cruise control without hardly ever having to even touch the brake pedal. That really gives you great mileage.
If the highways in your area are very congested, you will not see a big improvment in your mileage simply because of the traffic and the constant speed changes necessary.
A 4300+ lbs truck cannot be expected to get mileage like a Honda Fit, etc, and your mileage sound very reasonable for the conditions you are probably driving in.
...Richard
