I have a 2013 RM-Z250 with 11 hours on it. I ride 40+ Novice so I am not very hard on my bikes and I keep up on scheduled maintenance. Since I got the bike I would very rarely not be able to upshift to 4th or 5th. I would try shifting hard several times and it was like you were in 5th and couldn't shift any further but the bike was in 3rd or 4th. Lately it started doing it really bad. If the bike is cool and I just put I can run through all the gears. Under any power, even if I pull the clutch to the bars when shifting, it goes through 1-2-3 then it just won't go to 4th 80% of the time once the bike warms up. I tried some heavier oil (I was running MX530) and moved the shift lever around for kicks and nothing. Tonight I had my friend help me split the cases sure it was a bent shift fork. After getting to the shift forks and looking at everything, all 3 forks are straight with no wear as are the pins they ride on. The shift drum has a solid positive feel and all the grooves are in excellent condition as well as the pins on the forks that ride in them. Honestly, everything looks new as I would expect with such low hours. I wonder if this could be from being assembled incorrectly at the factory or something? If anyone has any advice on this I would greatly appreciate it. I am lost and don't want to put it all back together and still have the same issue. Cheers!