I RUN BELT DRIVE BOBCATS AND WE HAVE TO ADJUST THEM OR REPLACE WORN BELTS.NEVER RAN A TORO SO IT MIGHT BE DIFFERENT ADJUSTING THEM.TAKE IT TO YOUR DEALER THEY'LL SHOW YOU. ALSO CHECK THE INSIDE OF THE BACK WHEELS AND MAKE SURE THE BELT THINGIES WHERE THE BELT RIDES ARE NOT DISTORTED FROM HITTING THEM ON CURBS ETC. MAKE SURE PULLIES ARE CLEAN ALSO.
i have the same problem, one of my traction belts vroke last season so i replaced both of them, then a month later it would not climb hills, i was wondering why they were going so fast and adjusted the t-bar adjustment, but it kept getting worse. I went to my dealer and he said there is a bolt under the transmission that can slide in and out if you loosen it up and it will fix the problem. I havent tried it yet and am not sure how to do it but you might want to look into it.
Luke, ther are 2 adjusting rods on either side of the handles. Remove the wing nut, push the rod out of its holding notch, turn the rod so that it lengthens, place the rod back into the hole and replace the wing nut. This will give you more tension on the drive belts and should solve your problem. You might take a few times to get it just right.
Also, after you have the belts properly adjusted (not overtightened), go down to the automotive store, and get yourself a can of what is called belt dressing. There are several different brands, and Permatex is one of them. With this belt dressing, you are only going to squirt a SMALL AMOUNT on each belt. You only need to cover about a half inch of the belt, as it distributes when the belt goes around. The only thing is, is BE CAREFUL when you first run your mower, because it will act NOTHING like you've experienced with your mower, before. It will be so responsive, that it will literally "jump" when you let out the handles. I guarantee your mower will walk up any hill that the tires get traction on. I hope this helps.