So you know how people like us know our cars intimatly, and can tell when thigs are going wrong before they do, well things are going wrong.

04 cavalier auto, 45,000 miles

Car idles a tad high than before, (600 rpm instead of around 400-500).

The fuel filter was replaced 30k

Oil and filter changed every 4-5k miles with mobile 1 synthetic and FRAM oil filter.

Oil was last changed at 43,000 miles.

Air filter was last changed at about 28-30k miles with a k&n drop in filter.

Tire pressure checked every other week.

Problem is this.
MPG is starting to suck, getting 28mpg rather than my usual 33mpg though no driving habbits have been changed

And acceleration feels really rough. Like the engine is having massive vibrations whenever i step on it, but once I am up to speed there is no problem whatsoever, the engine is smooth again. No CEL lights or anything.

Help me out thanks!

The only thing that has been changed recently, was an optima battery was installed as well as a new amp, HU, and speakers.

I'd try a few bottle of fuel system (or injector) cleaner. Also try pulling the plugs and see if any are fouled or something simple.