All the "numbers" are not in yet, but here are some things I did "on the cheap" for my '96 4x4 extended cab long-bed (heavy) with 3.9:
NAPA "brass" dist cap and rotor: $14
MSD Blaster replacement coil & Taylor 8 mm wires, Truckpermformance: $100.55
Clean and oil K&N filter: $0
38 psi in all tires: $0
Total, less than $120 including tax and shipping where applicable.
MPG in-town +3 mpg (12 to 15) --25%--BEFORE wires installed and air cleaner service.
I have been checking mileage on one tankful after each change I made. Increased about 1 mpg after the new dist cap and rotor, 1 mpg after coil, 1 mpg going from 34 to 38 psi.
I drive pretty much the same in-town routes at similar speeds between fill-ups, so the figures should be fairly accurate comparisons.
My plugs are the standard Champions, and have a few thousand miles on them.
I'll post the final in-town figures--with new wires and air cleaner service--after I fill up this week, and later when I get some all-highway miles in on a tankful. (Running 87 octane unleaded.)