When i bought my wizard lawn tractor back in 08 it drove fast and worked good. Now its just falling apart. It doesn't go nearly as fast as it used to and has problems getting over the slightest incline. i need it running good for the winter ahead. The carberator has been messed with a few times. Could that make the tractor drive slower than it used to. The transmission is fine, i checked that but i'm not sure on how to give the tractor more pushing power. what should i do???