hi bryce
I have the same mower with the vsx160 engine,there is not much difference between slow and flat out.the motor will rev out under load.try a hot restart, then you will hear some revs but i feel the same as you said about the governor.now that my mower has had a bit of use i am now trying ultimate 98 octain pump petrol [BP] with valvoline formular V semi syn oil at 25to1 mix it seems to rev a little harder ok bryce cul regards graham