Gas Mileage Improvement !

When I got my new to me car,(95-E420) the first thing
I did is monitor my gas mileage.I'm kind of disappointed
of the results.I used to get 15-16 1/2-city and 22-23 mpg.
a/c off.Another thing that concerned me is the eng.temps.
At 65.F the temp goes to 105.F in a stop and go situation,
so I ventured a little bit.I gap the plugs from 32mm-40mm.
At 40-good starting,good idling but no highway grunt.
At 38-good starting,good idling but the power is like at 32.
The best for my car is 36mm.silky smooth idling,good starting.
very good highway passing power.To deal w/the warm temps,
I added,watter wetter on a 50-50 mixture of H2/0 and MB
anti freeze.Lastly,installed Jim F's "Cool Harness".What a
difference little things can do.My engine never saw 100 anymore.
Gas mileage now is.17-18+ city the best in a highway is 25+.
Driving habbits is the same and same brand and grade of
gasoline.

Could it be the plug gap? The Watter Wetter?
The Cool Harness or The cool weather temperature?
Anyway,I'm a happy camper.