I have a big box store JD L110 with 157 hrs on it (purchased new in 2003) I have a fairly steep yard and the mower has been getting progressively slower at climbing the hill, especially the longer a mower session goes.

I recently had someone look at it and they replaced the pulleys and belt that feed the drive system.

Now, after the 2nd mowing, the same high pitched whine comes from the rear end. It seems the longer (hotter?) the mower goes the slower it is until it stops moving forward in high grass or up the hill.

Is there something else I can look at or is a new transmission the only option? If a replacement is needed, any ball park cost and can it be installed by someone who is reasonably handy?