Thanks for all the detail, it makes helping so much easier.
So, did you clean the carbs before or after this occurred, your timeline is not obvious.
Did you test the two limiters (reverse and PB) separately or together? They actually limit at different RPM's, reverse being somewhat higher - so doing both at the same time will give you the lower of the two only... try unplugging the reverse wire only, if you haven't already, and see if THIS is the same RPM you are having problems at.
Does your reverse light work normally? If so, any chance that the light is flickering slightly when this happens? Vibration induced by certain RPM's can cause the reverse switch spring connection to break contact briefly, turning the limiter on intermittently - try grounding the wire and see if the problem goes away. (I'd guess, from info so far, that this is the most likely culprit)...
'01 660 Raptor, Burgard +2+1 arms, YFZ Shocks, LSR anti-vibe, CTR pipe, jetted, K&N
'01 Polaris Scrambler 400, K&N
'02 Honda 400ex, Big Gun pipe, jetted, K&N, Lonestar +2 A-arms, Lonestar anti-vibe
'04 Suzuki LTZ400
'16 RZR XP4 1000 Turbo