2016 Grizzly Diff Lock question

I rarely have had to use the diff-loc on the bike but we got some snow the last couple of days and decided to engage it and take a blast down the road. I noticed right at 20mph the motor started to retard, like it was hitting a rev limiter. Is this normal ? Not sure if it was doing this cause I still had decent traction and all 4 tires were not spinning? Any insight would be appreciated.