Scotts 1742 Transmission Issue?

I have a Scotts L1742 and it started acting weird when driving.  Engine runs fine but something with the drive train seemed off.  It was almost like something was slipping and it sounded like the tensioner was slapping around.  The belt was old so I ordered a new one and once it was installed, same thing.  Everythink looked normal so I used it to mow the lawn.  It acts up mostly in faster gears (4 and 5).  When I was mowing it would barely go when it started to lose traction.  When the limited slip engaged I realized that is the sound I kept hearing.  Weird thing is it is happening when just driving on flat ground.  I assume something is broken/worn in the transmission.  It is a Splicer 4360-149.  Does it sound like something to repair or should I find a replacement transmission?  Or get a new mower?