1989 454 crew cab dually

I've bought this truck last year to haul a racecar with and it is in good shape. First time I hauled my open trailer to the track I noticed that this fuel injected 454 has no power. Also it only gets about 5-6 mpg even without the trailer, it just s ucks the gas and lacks power. I've installed a new fuel filter, plugs and wires without any results. The truck idle's excellent, but when I'm taking off from a stop sign/light it hesitates until it gets some rpm's then cleans out. The check engine light doesn't come on so I dont know if the computer has any codes in it, nor do I know how to pull them either.
Anyone have any suggestions on what might be wrong with this thing? It's also my daily driver and going 20 miles to work one way is starting to get expensive
(1/4 tank of fuel just going to work and back home)

you have to think of the gvw (the weight you're moving around). My dually is over 10000lbs.
It gets 11mpg, but i've been tweeking things.
But not with a programmer, though.

Understand this if you can-- My 2004 dually 4x4
crewcab gets better gas milage with my gas cap off!!!! ( put it back on when parked!)

If anyone else understands why, please reply.
Also, if you know of any problems that I may face
by doing this.

Hint: vacuum

My first truck was an 89 ex-cab dually with the 454.
I pulled a 10,000lb steel horse trailer alll the time with that truck. I experienced similar problems with mine. The truck "Big Momma Dually" got about 7mpg on the freeway or in town and often ran hot. My truck also seemed to lack power from the start, but then gained power up through the RPM's. I went through 3 motors in this truck before I finally gave up on her and sold her last month. Never could figure out what was wrong with her.

Good luck!