Small Engines (Lawn Mowers, etc.): Cud LT1042 hydro question, debri, happy medium

Question
I have a cub LT1042, recently it has began to move alot slower in forward. When I adjusted the linkage I lost reverse so I adjusted it back to a happy medium. Is this going to be and adjustment  issue or a drive belt and or idler pulley issue? I haven't dropped the deck yet to see if the idler pulley may be stuck from debri or needs lubing thats in the plan. Thought you might be able to point me in the right direction to start. The mower is approximatley 4 years old and is cleaned after ech use and stored ion the garage. Thanks for any assistance

Answer
Some models have a drain on the transmission but I need the mower model and serial number to check which unit you have.  The model number is located on a sticker under the mower seat.

Are any of these model numbers below your mower?

13BX11CG710, 13BX11CG709, 13BX11CG712, 13AX11CG710 LT1042, 13AX11CG756, 13AX11CG709

Eric