2008 Ultra depressing

You need to do some tunification to the motor.

Put on stage 1 air filter kit (ness big sucker or HD SE Kit)
Set of slip on mufflers or true duals with mufflers like Reinhart, Samson, V&H

Then tune the bike for better mileage.

Best bet is a powercommander or HD SERT (Screaming Eagle Race Tuner)

Have it properly dyno tuned, tell them you want power when WOT but mileage when cruising, and give them the cruising RPM and speeds you run.

I have a bud with a 103 that gets 46 MPG at 65 MPH loaded and another on a 96 inch Street glide that does similar numbers.

We setup the AFR in the cruising throttle position and RPM to have better milage about 14.1 to 14.3 AFR and we have more fuel at WOT.

If you want to do the SERT yourself you need a Daytona Twin Tech system which has wideband o2 sensors you put in the headers, and then ride, record data , set the cyl V/E in each cell properly, then tune the afr.

Or pay a good dyno tuner to get it done.

It's an 800 pound bike with you on it and the frontal area of a brick,

RIde it hard and eat gas, ride it average it should return better mileage.

For more power drop in a mild street cam, Woods Performance 6-6 for late model twin cams with the new cam design (07 and up) is a great street cam it will make a big difference and you won't have to do a lot of machine work.