tune up time

so I have put about 2000 miles on 96 rmw 2.93 rear 75000 miles young, and have been getting about 12 mpgs on 20 mile hwy drive to work. decided it is time to try a tune up.  looked over vacuum lines and don't see or hear any leaks, also hear no exhaust leaks. I orderd the following ac-delco oem parts...fuel filter, platinum plugs, wires, cap and rotor kit, coil, pvc valve and grommet(was loose fitting)  My first lt1 so I am unsure if it has the power it should have or not, but it will roast the tire right off. Seems to run good, do hear a slight flutter in ds exhaust at idle. Any thoughts as to what else to look at would be appreciated.

Oh yeah I almost forgot, Also picked up a real nice set of SS wheels and 245/55/17s to complete the tune up

Thanks, I will post some pictures when I figure out how

scan it and see what the O2 mV are doing. 12 mpg is pretty bad. Make sure you don't have a binding caliper or something else that might be affecting mileage.

Replace the O2 sensor & make sure your tires are at 40psi.