That's what the mechanic in me thinks also, but after reading - https://www.lawnmowerforum.com/threads/is-ztrak-m535-a-lemon-hydrostatic-drive-is-failing-w-only-245-hours-on-mower.72519/ - where he says it's bad for the hydrostatic drive to run it below full throttle, I had to ask those who know...