K&N makes a filter kit that replaces the stock air box, it really helped my 89 with the 4.9L. Opening up the exhaust with an aftermarket muffler and new, larger tail pipe didn't hurt it either. Gears are a great way to pick up pep, but not always great on mileage. An MSD ignition is always a nice upgrade, there are tuners available too.
I'd suggest starting with a good tune up, plugs, wires, filters, PCV valve and see what you think from there.
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