I have a 2008 420 Rancher ES. It would grind going into 4 th gear. I went in the transmission and replaced the 4th gear, gearshift drum and fork. Installed the engine back into the ATV. It starts up and you can change through all the gears when the ATV rpms are low. Once you start increasing the rpms and shift gears like normal it, the atv cuts off. Doesn’t matter what gear you are shifting to. The temp light and the FI light come on and it displays what gear it’s in. You don’t have to cut off the key switch to restart it. It cranks right back up. Replaced the battery, removed and replaced grease for the gear motor shifter, reseated connections. I also ohmed out connections for sensors. Not sure if the problem is electrical or mechanical and if I need to go back into the engine. Any help would be appreciated.