If rest of tractor is mechanically sound plus you are mechanically inclined and have the time, Duane at Tuff Torg will walk you thru the process of upgrading your K46 to K57 specs— if your tranny needs rebuild parts will cost your about 250 to 300 bucks plus another 100 or so for K57 parts. If you don’t have the time you can ship entire transaxle to Duane and he will do upgrade for you- somewhere in vicinity of 600 bucks – but at end of it you will have k57 tranny ( that you can change oil on without removing tranny) and increased torque – if I may ask how many hours do you have on tractor? Do you mow hilly terrain?