These only go so fast and are usually are already maxed control wise. If you are having slower than normal speeds then the unit needs rebuilding.
From Tuff Torq>
Loss of Power
Replacing Worn Cylinder Blocks and/or Center Case
If your transmission is having loss of power or no drive when it reaches operating temperature, it is likely that the cylinder blocks and center case need to be replaced. When replacing any of these components, it is critical to replace all components to include 2 cylinder block assemblies with new pistons and springs, and the center case.
If either the cylinder blocks or the center case has damage due to wear, then the associated parts will also have some degree of damage. If all are not replaced with new parts at the same time, it is very likely that you will have another failure within a short time.
There are many misguided blogs on the internet that say you can save money by not replacing all components. While this will likely work initially, it will result in a much earlier repeat failure than if you had replaced all recommended components. At this point, you cannot simply replace the components which you avoided in the first repair, as they will be damaged and you will still have to replace them to properly repair your unit.
We offer a complete repair kit that includes the center case, cylinder block assemblies and all gaskets, filters and sealant required to complete the repair.
End of Tuff Torq quoted info.
Also you need the serial number of the transaxle as there were three different K57R used,