What year and model ATV do you have? Just curious
It's a 2004 TRX400FA (Rancher 400 AT). Having the Hondamatic probably makes it more sensitive than others.
This thing has always been like having cheat mode on hills. Climbs anything. But not yesterday. I got stuck on a rocks going up a hill a few times. It wasn't fun.
I'm assuming it's the oil because I changed it Saturday and it was fine before that.
Rustler, I'm one of the few remaining regulars with the 400AT. Been running Rotella T6 now since I put a new clutch in 3 years back. I also mix in at 5% Lucas Heavy Duty Synthetic oil stabilizer. I picked that idea up from Melsman a while back. The added zinc helps cushion the pistons on the swash plate. Last thing I did was make my fan controlled by manual switch, so I can run it as soon as engine gets warm. These 400AT's run the oil really hot and without the fan running they can get too hot way too easily, which is how I smoked my original clutch, fan didn't turn on cause the oil temp sensor stopped working.
EDIT: There were a couple years where I ran the Valvoline oil. I don't remember it ever being any different than any other kind, because I think for quite a few years my auto tranny wouldn't shift properly because of a slightly slipping clutch. But when the clutch really went out was when the oil temp sensor stopped turning the fan on. To be safe, I would just run Honda oil or Rotella T6. Ever since my new clutch and running good oil, I've had zero issues whatsoever with the autoshifting.