Ok.. this is getting pretty ridiculous!
Heres teh story, after changing just about everything in this 2000 Maxima.. Coils, MAF, clean throttle body, alternator... Car runs great for a couple days, then slowly but surely goes back to s*** gas mileage, and poor acceleration.. I was told, MAf sensor.. again.. So I changed it... with an aftermarket one.. Ran Great.. Again for a week or so, but slowly back to poor acceleration....
Went to Nissan, spoke with a tech there, said go with Nissan OEm MAf sensor, so I bought it right there.. he said install it, and if it runs good, dont worry about ECu Update/reprogram.. It did, so I didnt...
Now 6 months later (and has been going on for some time, about 2 months) s*** acceleration again! I swore Knock sensor, so sim'd that with a 470ohm resistor, running good, but still not accelerating like it should, and shifting hard at 4k rpm, and wont downshift to pass!
For s***, i reinstall original MAF, and runs great, A little laggy from 2k-3500k, or jumpy acceleration, But it accelerated!Nicely actually!
For s*** and giggles again, I even trued the Aftermarket one! Same thing! WAY better Acceleration with a couple little surging or laggy spots in the acceleration curve, but overall, MUCH Better!
What is the deal with this car???
SOMEONE PLEASE HELP ME!!
Now..... Im a Helicopter Pilot, and have worked on many aircraft, as well as cars, and like to think I can figure these things out.. But this car has me stumped..
Its like it accepts and runs well on the new part, in this case the MAF sensor, but gets used to it and "Bored" with it, for lack of a better term, and decides to slowly go back to running sluggish again after a week or so.. Im leaving this aftermarket one in, because it felt the best of the three... for now...

Are you using oil based air filter like K&N? It can easily gunk up the air intake.

I am not using K&N filter at all, just a paper filter... I actually got Nissan to replace the MAF under the 12 month warranty today..Installed new MAf, and car has some acceleration back, although still seems like its missing its growl! I have an APPt to get the ECU reprogrammed tomorrow.. Will post any noticeable results..