Newly acquired tractor and mid mount mower. Just got the tractor running a couple days ago. Everything seem to be working fine, except I have not figured out how to engage the mid PTO to drive the deck. In the LOW position only the back PTO turns. When I try to put it in the HIGH position it wants to grind. I have the speed control in neutral, clutch depressed, engine running, brakes on. Something I am not doing right. Manual for the tractor or mower was no help. Somebody please clue me in.