Geez! With 4 year old fuel I'm shocked it runs at all much less great.
Aside from ShiftingSky's advice (which should be heeded). You already did the Bat, belts and fluids so I'd say regular "tune up" stuff like plugs/wires/cap n rotor, air and fuel filters and PCV valve should be next in order.
Ever meet someone that accidentally bought a set of 35s?
They call me Birddog. Master of the Sawzall.
35x12.50x15 BFG A/T on Legos
De-Plastified and Blacked out