YT 6800 Transmission

[HWM]

Greetings Folks, My YT 6800 has a transmission problem that I hope has an easy fix. The transmission runs great when it is cool or during the first ~20 minutes of operation, After everything is up to operating temp the transmission surges. The forward shift handle is fully engaged and the engine is at WOT but the tractor just slows down to a crawl then after 2 to 5 seconds it emits a chirping sound that sounds like a power steering pump that is low on fluid, and then the tractor accelerates to full speed. It then travels ~ 100-150 yards and then goes through the same cycle of slowing down , chirping and re-accelerating. The reservoir for the transmission is full and looks to be clean. The screen inside the reservoir is not clogged and has no debris in it. Any Ideas ??? Thanks for your time and effort in advance. Thanks, Hugh...

[rattosh51]

HWM,
 Welcome to the forum.
I haven't heard of this one before. I guess the main question would be, when, if ever, has
the transmission oil been changed? If it has never been, that's where you would have to start.
Yamaha only put in standard 10W30 oil in there from the factory. Make sure the drive belt is in good shape too, could be slipping...chirping sound could be the belt?