I keep a spreadsheet showing what I have done to the trike and the resulting MPGs and/or performance and have since it was new and stock. Mileage was around 33.5 average stock.
I installed a slightly modified stock head pipe to get rid of some felt heat(won't admit to losing anything out of it), and some Screamin' Eagle mufflers. Mileage increased slightly over stock, probably an average of about .5 MPG. Also put on a K&N air filter and external breather from DK. It didn't seem to run as well and seemed to struggle some with 2 up at freeway speeds. Quite a bit of decel pop. Also tried some VIED 10s in here somewhere, but not impressed.
Bought an FP3 and installed it using Power Duals/Twin Slash Rounds as the tune as per Vance and Hines tech. Performance got much better, although still not great. Mileage dropped to about 32 MPG average. Still some decel pop, but not near as much except when hot.
I had purchased some Thunder Torque inserts a while back, but never used them. Thought, why not try them? I installed them about 1/2 inch back of the baffles. Absolutely no decel pop. Mileage increased. Sound from the eagles went from a bit obnoxious to just about right. Next two tanks increased from about 32 to 34 MPG. We took a trip to Branson from SW AR Memorial weekend. Mileage varied from 34 to just under 39 MPG. Average was just over 36 for the trip.
I can't say that there was a huge noticeable increase in torque, but I did find that it was not struggling on the interstate like it did before. It ran great through the mountains, but this was the first time I had taken it there, so I had nothing to compare to.
I have not done an autotune, but if it continues to run as it does now I probably won't.
Nothing scientific here. Just some observations.