Final update - took it to a shop and determined it was a bad plug. I had replaced both plugs a few weeks ago, but apparently one was bad. Guy at the shop identified it as soon as I fired it up and backed it off the trailer. He said it sounded like it was only running one one cylinder initially, and then the second one kicked in a few seconds later. Probably why the issue was intermittent (sometimes struggled and other times didn't). Shop replaced the bad plug and ran it for a while to confirm everything was okay. Didn't charge me too much for the simple fix

. I ran it for 3-4 hours this weekend and had no issues, so at this point it appears the issue is resolved.