CM2350 Reprogram help

[Carl G]

I’m having problems (I would think) with my 2016 389/cummins 2350 set at 500 (deleted)
13sp, 3.36s and 24.5 tall rubber.
Pulling VAN always 70k-77k

Sometimes I get a 25% de rate in 3 hours message.. goes away within seconds.
Also my mpg seems to be closer to 4 than it is to 5!!!
It used to do way better then I think gradually began doing worse? I didn’t notice because I’ve been running the crap out of it 75+ careless of fuel economy on a run I had where time was more important.

Now I can’t seem to get over 5.5 not even at 65mph? I used to get 6+ at 65mph
If I run 70 I’ll be low or under 5s
I’m mechanically inclined, had a leaky CAC, replaced that. No leaks anywhere, no mechanical issues as far as I can tell.

On the pics the computer does a little “better” than manual calculation by about .2mpg

Truck will idle funny in very cold weather.. but once it’s up to 185f or so it works fine. No smoke, boosts close to 40 if I lean hard on it.

Seems I try to run around 10-12psi and it starts slowing down to maybe 50mph?
Pulls like a freight train.. plenty of power in mountains.. just poor “speed maintaining”? Idk if I’m coming across.

Probably does the same mpg across 64 and 77 in WV than I do in flat lands of OH IN and IL.

I have a diagnostic laptop and Calterm but idk how to use it. Could probably be checked or reprogrammed remotely? Any help is appreciated. I’m happy to pay for services.