Been riding tikes off an don for a few years now and have come to accept they just don't get good mpg. It's life on 3 wheels.
After getting our 2015 freewheeler I expected nothing less than low mpg, 30-34mpg is what I am use to getting. 34 being on the high side and ridding easy.
My first couple of tanks were spot on 30-31 mpg as suspected.
Had to ride to town to pick up the back rest. Filled up and, get this, I got 37.7mpg. All I could say is wow.
Rode to Chattanooga to thunder creek, around 50 mils one way. Rode mostly interstate due to it getting late. set the cruise at 80 mph and enjoyed our ride, my wife won't let me to go to a HD shop unless she is wit me. I can't be trusted there. lol
Rode back home doing 80-85 mph, getting close to dark. Don't do riding on the mountain after dark, just not safe on a trike or bike. Too may varmints.
Stopped to refuel. Almost fell off the trike. 99.9 miles with 37.1 mpg, 2 up.
My 2 wheelers don't do much more than that.

I brake in my engines in a certain way. 2 heat cycles, then varying rpms between 2,3500 rpms to 2,800 rpms for the first 500 miles.
Power is good up to around 3,500 rpm's then it fades some. The power is still good but the quick pulling has slowed down. It's the cat and ac plus lean tune. Once I get enough miles on it I will do a catless header with a open ac with a good tune. That should solve that. I never do a stage one or tune until around 4,000 miles. I always tune when doing a stage one. So I wait so I only have to do just one tune. You do em to early you have to retune later.

 

I have about 700 miles on mine. Mostly 2 lane riding, 60 to 65. I don,t use 6th gear until over 60. My last tank was 36. I have been breaking mine in similar to you. I agree on the cat. I am thinking about replacing the header pipes with catless. I would like to see how that runs with the stock mufflers. I would also like to get the power vision with auto tune. I have also noticed that the more miles I put on it the stock mufflers are getting a more rumbling tone

 

If you click the link below my signature pic, you can see my mpg results for every tank I've filled. The app is called 'Fuelly'.

 

Got a little over 12,000 0n my Free. Average 35 mpg

 

freewheeler trike: catless headpipe, performance mufflers, stock AC, EFI download, 34.7 MPG. Good power till about 4700 RPM.

 

Have just under 7000 miles on mine and don't have the slightest idea what the milage is. I do smile a lot though.

 

So then it seems they are prone to better mpg than most trikes.

I usually do a catless header first to see if I need/want more volume.
So far I haven't needed to change the mufflers, the cat added enough volume to suite me.
The 254 cams are a good low end cam with some good mid range. Not so much on upper rpm's though.
Around 4,000-5,000 miles you will notice a improvement in mpg and power.
So far I am very happy with this trike.

 

When I got my tuner installed, the tuner guy said power takes fuel. More power more fuel. So if you stay off the throttle you will get good mpg. Going up hills, turning of the throttle, etc., uses fuel. Put in cams, mufflers, etc., more fuel. Seems to make sense to me.

 

Yes this is true up to a point.
I have built a lot of HD engines, including big bore with big power. It is the power to weight ratio. higher tq engines will get better mpg than one built for HP. Good tq takes a lot of stress off the engine.
Example:
pro twin 113 built for tq. 124 hp/148 tq I average around 45-48 mpg with normal riding, Dyna super glide
SS106 built for HP, 115hp/110 tq, I average 38-440 mpg normal riding, wide glide.
On a HP built engine you use upper rpm's for good power, but with a engine for tq doesn't need upper rpm's to pull good.
This is my experience yours may differ.
I would love to have the 113 in our flrt.

 

What cat less header pipe are you using? Thanks.