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a Taller fifth gear can do an enormous amount for your mpg.
If your Del Sol is stock then you're doing a good bit over 3K rpm in 5th just to stay the speed limit on the highway/interstate and any higher speed backroads.
All reciprocating engines are much much less fuel efficient at higher rpm. The problem is everything has to happen much faster. . .and it doesn't. Just because you can make the engine run at 7K rpm doesn't mean the dynamics of the event are going off right. The shorter your expansion stroke(overall time) the less time for the gas to absorb heat and expand, this is why Torque graphs usually peak out before HP
(and its usually about 2K rpm lower Del Sol I believe max ft-lbs is 4100 rpm and horsepower is I think 6300 rpm).
Engines do have a power band that they are strongest through. . .but they are not fuel efficient in that region for reasons mentioned.
Swapping your trans to a 5th gear that lets you do 65 at 2.5Krpm or less, filling your tires to 38-41(wherever your max sidewall is) PSI, dumping any extra weight and not running your AC will definitely get you to at least 35(assuming your exhaust system doesn't have a leak somewhere).
I get 35 with shorter gearing than stock, and if I had a taller gear I could stay below 3K rpm on the highway(3K is about the breaking point for FE on the Del SOl, lower and its really good, higher and it starts disappearing fast).
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