Jason, if the engine does not slow down and the mower does, the belt or clutch must be slipping. The involvement of the clutch pedal feel suggests it is the clutch, not the belt. Also, the behaviour of the clutch pedal suggests it is a linkage problem rather than the clutch itself. The clutch linkage is most likely either worn or needs adjustment. It sounds as if you are pushing the pedal all the way down to get any drive, and the linkage is on the verge of going over-center somewhere, so you are not getting proper pressure from the pedal to the clutch plate. It might be that the screw-adjustment on the end of the pull-rod is wrong, and this is causing the over-center action. If not, there may be too much lost motion due to loose joints. Can you take a look at the linkage, try to find somewhere it can just about go over-center, and post pictures of it please? Once you find where it is happening, we can talk about how to fix it: whether it is a matter of adjustment, or too much lost motion due to slack.
