I have a troy lawn tractor 18 horse 42 inch cut. I have replaced the belt on the deck several times always buying the same belt. The last two times I replaced the belt , the belt seems to be to long for the deck. It is loose and does not tighten up right when the deck is ingaged causeing the blades to slip and stall and stop cutting. All of the working parts of both the deck and tractor seem to be in good working order and not worn out. Is there a way to adjust the deck it self or does anyone else have or had this problem and know how to fix it ? My local service center doesn't have a clue what's wrong.

What's the model # of the mower? Might need serial number too.