Grizzly 300 Automatic Help

Just bought a clean 2012 Grizzly 300 Automatic with ~20 hours on it and am having a few problems.

"Bear" with me here, I’m new to ATV’s!

It ran great when I test drove it. The seller said it had been sitting for awhile, so when I got it home I drained the tank and flushed it, then filled with non-ethanol gas and a dash of Sea Foam.
It ran great after that, very smooth, for about an hour.
Now it’s dying on me after starting and I’m getting a rough idle once it catches.

Also…
when putting into gear sometimes, it will start to cough and stumble as though out of gas. Switching over to reserve clears it up, however my main tank is full and I can switch back to it and it will run fine. Fuel tank strainers looked fine when I had the tank valve out.

It seems to really bang the clutch when engaging at times. Sometimes smooth as silk, other times CLAAAACK!!!!! Is that normal? I know the centrifugal clutch functions on engine RPM and am thinking this is probably a result of the bad idle. But again, I’m a newb with this stuff. I’ve been unable to find anything on adjusting the clutch.

Anyway, I’m trying to get this thing sorted out. I’m not finding much info on the Grizzly 300 Automatics. Any help is much appreciated!

Mike