I have a 2003 Mercury 40HP 2 stroke with onboard oil injection. (40 ELPTO)

Couple weeks ago when I was out the motor started hesitating when accelerating and at WOT. Kind of like it was starving for fuel.
I figured a fuel pressure problem so I replaced my old removable tank, fuel line, and primer bulb. i also replaced my external fuel/water separating filter.
A quick test after that produced little to no improvement in performance.

Thinking about taking it to a Merc shop for troubleshooting but would like to see if there is anything else obvious that I could check out first.

Hard to troubleshoot myself since I can only run it on the muffs in my backyard. Cannot seem to replicate hesitation while motor is out of the water. (at least from what I can tell)

Need some help on this one.