I've got a 2544 here with about 60 hrs on it. About 2 years ago and around 10 hours I modified the speed linkage unaderneath to increase the reverse speed. Over time I've noticed a decrease in performance in both forward and reverse speeds. Could it be that the linkage should be readjusted, or rebuilt, or could it be the transmission?
Hard to say without examining full range of motion both forward and reverse. You have to get an idea by working the pedals and watching where the linkage attaches to the hydrostat itself. Problems with the hydrostatic drive are very rare with these. Low oil, or improper filter usually causes no go. 60hrs doesn't sound like you could possibly have a problem with the oil, but I assume you checked that.
Tractors of the past:
2010 Cub Cadet Z-Force 44 fab
2005 Cub Cadet 2544
1979 Case 220
2003 Yard Machines 17hp 42" transmatic (crap-matic)