lost grond speed from 8mph to 5mph Hustler fastak superduty

[cle]

I have 2010 fastrak super duty 54, last summer I noticed going slower even though 25kaw still running at high rpm...I checked tension on hydro belt and pullies / dealer couldn't help me any...is there an adjustment I'm missing,

 

[MRCo.]

Loss is on both sides and a consistent amount?

 

[cle]

both wheels are going the same speed going straight and in reverse

 

[edd]

have you changed the hydro oil ? could it be the filters are stopped up?

 

[MRCo.]

So the issue is common to both sides, so it's got to be a common cause. What's common to the two? The oil and the drive belt. Start there.