I have an issue with acceleration and surging that I've been trying to get to the bottom of. When accelerating from a stop at a constant pedal position the engine is just groaning and very slowly accelerating. If I continue at the constant pedal position the Relative Throttle Position in the Torque app keeps ramping up higher and higher, sometimes up to 40-60, then all of a sudden the truck will kick in and start moving normally and the RTP will drop off instantly back down to the 10 range and the truck runs normally. I can get around this issue by pressing harder on the pedal. Also, while going a constant speed, whether it's slow like in a parking lot or on the highway with cruise control on, the engine very slightly surges up and down. I can notice it while driving because I can feel it, but I doubt it's enough for a passenger to notice if they're not really feeling for it. While it's doing this, the RTP is bouncing around slightly too with the pattern of the surging.

So far I've changed all the plugs and and coils (I did have some misfires, which are all cleared up now).
Changed out the TPS.
Cleaned the throttle body and MAF sensor.
Changed the fuel filter.
Changed the Purge Valve Solenoid (it was hissing some).
Checked around for vacuum leaks with a propane tank and hose (I think my vacuum is fine, it has a steady reading in Torque).
I've ordered a FPDM to swap out my original one. Not sure this is problematic though.
No CEL.

Any ideas on where to look next?