Doesn't want to shift because the flywheel is turning.
Sounds like the hydraulic T.O. bearing fluid is boiling causing a lack of travel.
Try bleeding out the fluid you have and try some racing fluid ( sil. based ). Call the T.O. bearing company and tell them the fluid you are going to use and make sure they do not have any seal issues.
Some fluids have a water content in them which can be boiled and turned to gas at fairly warm temperatures. You may have one.
Is possible you have a clearance problem that is agravated by the increase in temp.
Good luck, hope this helps.
