08 rancher esp shift problem

Hey everybody, first time poster here. I would appreciate any assistance with an issue I am having with my 2008 Honda Rancher 4X4 420 ESP (electric shift). I recently purchased it, and I am not familiar with the previous owner’s maintenance or driving habits. The ATV only has 500 miles and 32 hours on it. The problem is that I am having difficulty shifting into 3rd-4th-5th gears during appropriate shifting rpm’s/speed, however, if I decelerate considerably (drop rpm’s), I can then shift it into the aforementioned gears. Additionally, the gears do shift with ease and properly when the ATV is sitting and running at idle speed, and/or while driving very slowly (although as is always the case, it will bog down in the high gears until I can get it up to speed). When it is properly engaged in the 3rd-4th-5th gears, it drives well and always down shifts properly (probably because above mention scenario in that it is decelerating and the rpm’s are lower). In a nut shell, the issue seems to be upshifting difficulties when at higher rpm’s (?). PS- I tried clutch adjustment via lock nut/screw adjustment to no avail, and I have been riding bikes for about 40 years, so I am not shifting at improper speed or while accelerating throttle. Thanks for any input. God speed and a great New Year to all!