Small Engines (Lawn Mowers, etc.): Troybilt Transaxle, variable speed drive, drive pulley

Question
I have a troybilt riding mower ( Model #  13AN779G766 ) that has a bad trasaxle ( slipping going down hills etc. ) I will be purchasing a new one and was wondering what kind, if any oil/Lubrication should be used etc. Also are there any special steps to installation other then bolting the new one in and reattaching cables and lines. Also this is the second time this trans. has gone bad on me, is there something possibly wrong with the clutch that causes it not to enagae properly? I've notice somtimes when changing from forward to reverse or opposite the lever does not move smoothly and needs to be forced. Sorry for the lengthy question, any feedback would be greatly appreciated. Thanks

Answer
The new unit should come filled with lubricant as these are sealed units.

Generally the gear boxes are pretty durable.  How steep are your hills?  

As far as parts that do wear on your unit the variable speed drive pulley bearing can wear which could put more stress on other driveline parts.  Have you ever replaced the drive belts or greased the varialbe speed pulley bearings?

Eric