Kohler Command Pro 27 runs good until it loses power

Ok, there's quite a bit of background on this one so please bear with me. I chased a sudden loss/restoration of power for quite a while before figuring out that it was the DSAI system. Replaced with the coil kit to fix it and that problem is gone now. In the process of trying to figure out what was wrong with it, I messed around with a bunch of other stuff that I wish I had left alone. Now the mower runs fine without load and I can mow with it OK. The problem is that when I hit a patch of thick grass mowing at or near full speed, it sometimes wants to die and I can smell gas. I can back up and wait a second and it comes back but is not performing anywhere near its previous level.
-replaced fuel lines/drained and cleaned gas tank
-replaced carburetor
-new spark plugs
-made sure governor was set with the shaft fully CCW (WOT RPM @3700). Slight surging at fast idle.
-air filter/system seem to be clean
I suspect that this may be a carburetor issue but am not sure. The carburetor only has one screw and I've been hesitant to fool with it as I'm afraid I'll make it worse. I have a manual for this engine (CV-740S) but none of the carb adjustment procedures seem to apply to this carburetor. Any help will be greatly appreciated.

You have 2 circuits in your carb. Idle and high-speed. Sounds like you have a partially blocked high-speed circuit. Remove the carb and clean all the little holes in the carb with a small wire/s. Run it from the carb back to the bowl. See if that helps.

Thanks for the reply/advice. I finally gave up and took it to a professional. I'll be sure and post the problem and solution once I hear from them

After sitting at the exmark dealer for two weeks, I took my mower home after they couldn't recreate the problem. Took it to another mower shop and he couldn't figure it out either. Last night, I put the original carb back on it (cleaned it in the parts washer at work) and it works like a champ. Thanks for the advice.