About 2 weeks ago, all of a sudden I went from 15 mpg down to 11 mpg! Dadgummit! I also have noticed a difference in power. I used to have to be careful when pulling away from a full stop or going around a corner and accelerating at the same time because it would break loose and spin till the cows come home. Now to make it spin I have to actually try! This all happened in the last two weeks. Whats up with that?

 

Could be tons of things.But i would look into Failing Plenum Gasket.There is alot of info here on it.

 

^^^^^^^^^^^^^Thats what was going to be my first thought....failed plenum gasket. The next thought is to make sure all cylinders are firing, you should be able to notice this without any trouble. If you were towing or hauling or doing more hills, that could do it. did you reset your Trip odometer at the right time last time you filled up, ive done that before (waited too long to set it, like 40 miles). Make sure you have adequate fluid levels in the tranny and rear end. check your tire pressure. check your air filter, and plugs. Most likely its not one of these for that big of a drop, except maybe the towing and plenum, but it could be a combination of a lot of these. I know most of this is redundant, but sometimes it helps to hear it.

 

couldbe 02's the upstream 02 clogged up or going bad and adjusting your mixture to run richer..you can take out the upstream 02 and give it a good cleaning with special electrical parts spray cleaner.. and put it back in.. run some fuel injector cleaning system.. some seafoam maybe.. hows your cat? new/replaced or oem one? um.. time for a tune up? plugs wires cap rotor

 

I'm know it's not the cat - she's been gutted . Checking plugs and wires is on my list. And I'm positive she's pumping on all eight cylinders. How do I check the plenum gasket??
Another issue that arose recently is that it has to turn over an extra couple times before it starts in the mornings. Any connection there?

 

get a little mirror and flashlight, and look down the throttle body. if you see oil pooling up in there, its leaking.

 

Yeppers,Check valve in the fuel pump if probably stuck.I am having the same issue now.Usually requires pump replacement.But I read on here recently someone took the pump out ,cleaned the assembly to free the check valve and its been running great for them.If it were me,If I went through all the trouble to remove the pump.I would bite the bullet and go brand new why I have it all apart.Wouldnt want to do it twice