I just did the 50hr tranny fluid change on my 2800 HST. I jumped the gun at 45 hrs
. I wanted to give SUDT a try. So, I got it changed and mower about 3 acres of grass yesterday. I will say this: the SUDT cut out the HST whine completely in Low range and quieted it down by atleast half in Med range. I think it made the tractor pull a little better too. My rpms always dropped a little when I pulled up a steep hill while mowing, like 75 rpms or so. Now with the SUDT, I believe the the rpms drop about 50% less. These are marginal differences, but noticeable. This is my first HST and I never really got used to the tranny whine, but now it is gone mostly. I'm sold on the SUDT.