Need help with Hydraulics on L3750

[Davaron]

I had to replace the housing where the shifter lever goes into the top of the transmission under the seat. Quick on and off. SInce then I have had problems with the lift. Worked fine before I replaced the housing. Seems to work OK when cold but as it gets warmed up it will not lift. It will not sag down, it will hold but not lift. If you leave it awhile and let it cool down it will lift again for a bit then stop working as it warms up. I have replaced the filter and drained and replaced the fliud but no help. Any ideas?