. . . . . yes, I think you should get better mileage than that. I get around 32 to 35 in the city on my SE5 and I think that is very good. The upgrade has seemed to help quite a bit, but all the numbers are not in or "stable" yet.
BUT, I do something different on the tire pressures. The manual recommends:
Front (minimum) 13 PSI (maximum) 17 PSI. In non-summer months, I run 19 PSI and that is very firm for me. In summer, given the triple digit temps, I go to 14.
Back (minimum) 26 PSI (maximum) 30 PSI. I keep mine around 28 PSI year around.
I also have to drop my Jeep's tire pressure down ( I am usually at the maximum limit) in the summer or else I get an "Over Inflation" warning when I drive on hot days. Unlike Florida, I am also at a high altitude and I think that also effects it.
I wish I had more "data" on the heat effects and what you should run your tire pressure at, but maybe others in your geographical area can give you some of their experiences.
Keeping the tires firm will give you better mileage and longer lasting tires. The tradeoff is that the ride feels harder.
An unusual thing to look for is a gas leak. Check your gas lines and gas cap and make sure you are not losing gas there.
Tom