2000 max Acceleration and Gas Mileage issues

[jsta22]

I know theres been lots of talks on this matter, but would like to hear first hand what people think is going on..
My 2k max with 160k miles just doesnt have that VQ get up and go hard, growling acceleration! not since I bought it at 129k...
And Gas mileage around town is about 17-19mpg mixed mostly street, with some highway, and 21-22 max, with mostly highway..

Ive replaced plugs (NGK Plat), Coils (Twice!), MAF (twice), air filter (Paper), Bank 2 Pre Cat and topside O2 (still getting 430 code .. is an aftermarket cat) as well as new alternator, radiator, etc..

It just doesnt have that get up like I know these VQ's do!
I keep reading about possible Knock sensor needing replaced, but not sure of the exact symptoms... Or if its something as simple as needing the ECU reprogrammed with the new MAF..
I feel some days it has decent power, and easy effortless acceleration, and other days, even the same day after multiple start ups, it goes right back to running weak again..
Any ideas??
Only code throwing is P0430 for this POS Pre Cat which the mechanic is going to redo under warranty on the cat..
seriously about done with this car!!!

[Towncivilian]

Is there a fuel filter in the engine bay? If so, replace it. I'm not sure that'll help with the mileage issues, but it may help with acceleration.

[jsta22]

There is no fuel filter in the engine bay in the 2000+.. its under the back seat in the tank.. but No, i havent replaced that yet, but it is on my to do list.. its weird. Under light acceleration, it seems to go fine from first gear.. the problem arises while cruising at say 15-20 mph, and I step on the gas a little harder, there is a little more engine noise, but absolutely NO pick up at all, so press a little further, and NO pick up, not even an attempt at any more power delivery from the engine, although you can hear it trying a little harder...
It honestly feels as though its my MAF sensor again! but could this be so?? Its a 6 month old (Brand new) Nissan OEM MAF sensor! could it be bad already??
Also, could this possibly be why I keep getting the P0430 code in my Bank 2 for a Inefficient PreCat?? Maybe its playing havoc with that banks' fuel delivery???
Hmmm

[jsta22]

I actually got Nissan to replace the MAF sensor under the 12 month parts 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..