I am getting 8-9 miles per gallon the truck has new plugs new air/oil filters new plug wires.It also has a brand new fuel pump...it doesn't have much power before the engine warms up, even then it's not what it should be.

the fuel pressure regulator will not do it. you need to look at spark plugs ,wires ,air filter, fuel filter. tires pressure if tires are under pressure can cause bad gas mpg

use higher octan gas to see change air filter oil change will allway in most cases give a few moe miles on the gas

A tune up can reduce mileage. If they set the timing perfectly, that could reduce power and waste gas. You get the most mileage and power if the ignition is advanced as much as possible, until you get a pre-ignition ping in hard 2nd gear acceleration. They you know you have to back off a bit.
Fuel pump should get weaker with age, so should not cause worse mileage.
Air filter has much more effect on a carburetor, and little on a fuel injected car. But why not change it anyway?
If it idles rough, I would suspect a plug wire.

When is the last time you had a tune up? Have you changed the spark plugs lately? An often overlooked item is the air cleaner. A plugged air cleaner can take 3 or 4 miles a gallon off your average. You can purchase a K&N cold air induction or a cheaper brand, this includes the cleanable air filter and chrome air intake hose, replacing the stock. This should improve your gas milage by 4 or 5 miles per gallon.

could your driving habits have changed? or its in need of a major tune up like new air filter new spark plugs,pcv valve ,new plug wires ,an oil change and a fuel filter.

new plugs,plug wires,air filter,keep air in tires at 35psi,

Tune Time.
1)new spark plugs properly gapped.
2)new air filter (check every 35000 miles)
3)new fuel filter (every 35000 miles)
4)1 bottle of STP fuel treatment (red bottle) 4x a year.
5) oil and filter change (castrol or another good quality oil every 3-4000 miles.
6)proper air pressure in tires (check every 2 months
7) service transmission every 40000 miles or less.

New oil and filter
8) new plug wires every 80000 miles.

fuel pump and float

Lost gas mileage. I would have to assume that you are not getting the require mile per gallon. For example If the car book say 32 miles per gallon. You are getting about 20 to 25 miles per gallon.
If you want to improve the your gas mileage then you have to do the required maintenance
Oil change every 3000 mile
tune up as required
Air filter
If the wiring spark plug wire is old and crack then it need to be replace.
If you park out side and the batteries is about 5 years old have it check
If you buy the car new, you will have a car book follow the maintenance routine.
If you have done all the maintenance and the gas mileage is low than recommended then take it to a shop to figure out if some thing is wrong or not preforming as it should.
I do hope this help you.

Check the torque on your plugs, should be around 15 - 19 lbs - consult spark plug manufacturer on the torque - if you did not torque them enough, they may have become loose. Also check coil packs - make sure all plug wires are snug.