The wheel drive belts on my 2005 36" Toro walkbehind seem to be slipping. I moved the springs to the tightest position but the belts are still slipping, especially when using the left hand brake (mower wants to slow or stop when applying the left brake). If I turn left going up even a small hill the mower stops even after releasing the brake lever. The pulleys are spinning but the belts aren't moving. The mower tracks straight when no braking is applied. Am I diagnosing this properly? If so how can I fix it? Belt dressing since I have already tightened the springs? Other solution? This is happening in dry conditions, belts and pulleys look clean - usual dust, and the mower is only 3 months old with about 70-80 hours of use. I'd appreciate your help on this.