MPG keeps getting worse...

I bought my 2000 'Hoe about 2 1/2 years ago. It's a great vehicle, but the mileage is killing me. I understand that this thing is never going to get Civic-like numbers, but what's driving me nuts is the falloff in mileage since I bought it.

When we first bought it, we were getting around 400+ miles per tank. (18-20mpg). It's steadily been getting worse, and now I'm doing good to get 275 miles on a tank. That puts me in the neighborhood of 12-15mpg. Tonight I filled up at 214 miles and put in 18.9 gallons, putting me at a pitiful 11.3mpg..

It's got the 5.3 and about 109,000 miles. Since it turned 100k, I've been doing some stuff to get this figured out..

In addition to regular synthetic oil changes when prompted by the computer, here's what I've done:

1 - new plugs
2 - K&N Filter
3 - new tires
4 - cleaned MAF (didn't touch anything, just sprayed electronics cleaner)
5 - cleaned intake (spray stuff in my driveway)
6 - replaced leaking fuel pressure regulator (@ dealer)
7 - throttle body & injector service (@ dealer)

After steps 6 & 7, we saw an improvement for a few tanks, but then it went back to the 12-14 range and again, now I dipped into the low 11's..

It runs smooth, starts right up, doesn't smoke, smell or make any noises. The only symptom is my crummy mpg. I'm thinking there are a few other things that could be a problem..

1 - MAF sensor
2 - O2 sensor
3 - EGR system
4 - fuel pump (i.e. low pressure @ the injector rail)

Are there any other sensors or systems that I'm not thinking of? What order should I attack those things in (cheapest first makes sense..)

Any help is appreciated..

take to dealer and have work order wrote up regarding poor fuel economy...it has to get what it is rated at, if not, there is a problem. I've found over the past several years that those ratings on the window stickers on new vehicles are very accurate, whether its car or truck.....your tahoe should get 22mpg (cdn)

Definitly make sure that you change the fuel filter. It is a good idea to change that around once a year. It would make your fuel pressure go down if it is plugged up. I would definitly start there.