2005 GTP Poor Mileage... Please Help

[whitefeathersnpr]

I have a 2005 Grand Prix GTP with 80k miles. It is stock. Lately I have been getting rather poor mileage, often I am lucky to get 20 MPG on the highway. Occasionally I will actually get closer to 26 or 27 mpg on the highway. The car seems to have a hesitation in 1st gear it will kind of chug, then it will surge and over rev a little before going into second. When going down the highway the RPMs seem to be running a couple hundred RPM's higher than they should be (almost seems like it is struggling a little but there does not really seem to be a lack of power just revving higher than it should).
What have I done so far?
-Oil Change (complete with filter and synthetic oil)
-New Air Filter
-Fuel Injector Cleaner
-New Plugs and wires
-New coils
-Tires are inflated to 35 psi
-Have changed the oil in the Supercharger
-Run nothing but 93 octane gas
-Coolant flushed and replaced (thermostat and ECT both working properly)

Starting to pull my two remaining hairs out. Any help would be greatly appreciated.

J.

 

[NegativeOne13]

Have you looked anything into your tranny? Correct amount of fluid? Still nice and red and not burnt smelling? Have you ever done any maintenance on your transmission? If no, regardless if it helps your MPG, at least replace the filter and fluid, but I suggest NOT flushing it. Have you cleaned out your throttle body? Cleaned your MAF?

 

[whitefeathersnpr]

The fluid is full and red, not burnt. I have not cleaned the throttle body or MAF. Guidance on doing so would be appreciated.

J.

 

[NegativeOne13]

Pretty simple, Remove the intake duct off the MAF sensor, then unbolt your throttle body off the S/C body. There is a connector on the throttle body, remove the little clip then the inner part of the connector should slip up, then pull the connector off out towards you. Clean the throttle body out with carb cleaner, should be tons of black junk in there. Then for your MAF sensor, spray ONLY MAF cleaner on there. Inside you will see a mesh with two little thin pieces of metal then a needle in the middle. That is the part you want to spray and clean. So you will need to pick up carb cleaner and MAF cleaner from a parts store.

 

[whitefeathersnpr]

I have the carb cleaner so no prob there, and I can pick up the MAF cleaner. Are there any seals or gaskets that I will need to replace when doing this?

J.

 

[NegativeOne13]

The only gasket you will come across should be your throttle body gasket. You can replace it, but probably wont have to. Just be sure to take it off before you load it down with carb cleaner.