I sent you a PM, but I would not blame the FITech too much yet and recommend you don't just let it learn, it won't get there, none of them do. BTW, if you are on Facebook, there is an FITech page that you will likely get more help, but beware, skill levels and opinions are all over the place
I think you may need to get the timing in a better place in two scenarios, first is the initial/total at WOT, that's the easy part, especially if it has an option to retard during cranking. If it does, I'd have that engine at 22 initial at idle, 36 or so total, and all in by about 3000. If it doesn't have a built in retard for crank, then less initial.
The next part is where you get your mileage. The system should allow you to adjust timing based on vacuum, and if you can get 45+ degrees total at low load (cruise vacuum), your mileage will continue to pick up.
In the old posts, the guys poked at your intake. I am not judging your build at all, I'd run that intake in a heartbeat, in fact my 461 inch 4x4 is getting a ported EFI Victor, but at low RPM, even with less cam, there is going to be some mixture dilution from overlap and potentially fuel falling out of suspension. That is countered by more advance, especially at higher vacuum cruise
I'd also drop the idle down quite a bit. After all of that, need to make sure you have throttle plates set right for the IAC position and reset the TPS limits. In fact, any time you adjust any screw on a throttle body, remember to relearn TPS, it's how the ECM knows what your foot is doing
Additionally, make sure that the WOT and cruise AFRs are set right. I generally like low 13's at low vacuum, but you can let it climb at high vacuum, up neat 14.5 even, especially if the timing is advanced at low load.
In the end, it doesn't have an OD or lock up converter like your 6 cyl rocket, both drive the mileage up too, but I am confident that that engine has much more if you dig into it a little.
In fact, my hunch is that new cam, if anything, should have gained tire smoking power down low, a lot in fact, so I would have to guess there are some setup parameters the engine doesn't like. TPS setting, initial timing, rate, something.
Let me wrap it up that as others said, it's beautiful, I wish you were closer to Nebraska, I'd love to spend a Saturday dialing it in.