I recently replaced the plugs and they were way past due. However, that did not make a huge difference. I have Standard Load tires on the truck and the sidewalls are quite soft. I think that this may have something to do with it too. I am running 36psi and that is the max for these tires. I did not know that anyone made a standard load 265/75R-15 tire. Goodforayear does. The tires suck but they don't do bad in the rain and snow.

I should try some injector cleaner.

I recently remove my cap and put the tonnue cover on (this truck came with everything) and I will have to check the mileage again.

I am running 10w30 Mobil 1 (ususally use 5w but I had 5 quarts of 10w)
I have brand new 75w90 Mobil 1 in the trans, case and diffs.
I have no lift
I am fairly sure I have the 4.10 gears.