I'm new at this, but I'll offer this up:
I did the DPF/tune a few weeks ago, and installed 4" straight pipe..
before I even moved the truck, and while checking for exhaust leaks, I was astounded at the difference in exhaust flow.. that dpf must be hella restrictive.. it was BREATHING like I imagine a dang dragon would as opposed to being barely noticeable before..
i ran maybe two tanks through the truck before I did the delete, and saw two regens that lasted a couple seconds each- passive regens maybe? I dunno.. point being, my 44k truck likely was pretty clear in the DPF.. if your DPF is deep into it's service life, or is clogged with ash, you're choking that engine even more...
no matter how you slice it, the tunes produce more power, no? power in an internal combustion engine is only caused by one thing: more AIR moving THROUGH it.. if you're running 50hp more, you're pulling in and exhausting air that equates to that 50hp.. so, you are easily pulling more air INTO the engine to support that tune, but are you getting more OUT too? If you're not, you're not getting the extra power..
back pressure is a funny beast when it comes to back pressure due to physical obstructions in the exhaust.. you may have a barrier in your catalytic converter or DPF that flops about under low exhaust pressure, but when you amp up the RPM's, it has suitable power to move
the obstruction.. as a driver, that will feel like you're dragging a parachute or anchor, and then it all of the sudden lets you loose..
based on what you've shared, this is what i'm wagering on..
just wait until you drop that trashcan setup... and free the exhaust.. good stuff.. no parachute or anchor..