Just picked up a 2009 TRX420FA with 50 hours on it. Wanted to changed the oil since past owner didn’t keep good records. Picked up an OEM filter with O-ring and Honda GN4 oil. Before I changed oil I drove it in auto mode and it seemed to run well.

I changed the oil. Overfilled it a bit and drained some out. Cleaned up the air box and looked at the spark plug.

Now it seems to shift harsh on up shifts in auto mode. It even sounds like you chirping the tires on the pavement. No accelerating hard while noticing this. Not noticing this in manual mode.

I have the service manual and will look through it to troubleshoot.

Any thoughts on this, what to look at, or might it just need run more with the low hours? I have been checking the oil level and it right at the top mark. Seems odd that it didn’t act this way prior to the oil change. Unless I did something to something in the process of changing oil and going over a few things.

Central PA