800 Caseomatic proplem

[Zach81]

So my 59 800 will not work correctly work in Caseomatic as it just seems to stall out quickly after takeoff. Single disk lock up works fantastic. After much fiddling around I found out that if you depress the tredle and hold it down for about 10 seconds it will take off again for about the same amount of time that the tredle was depressed. It's almost as if the converter fills when the tredle is depressed. Anyway all pressure tests per the manual were done, clutch pressure -good, pump pressure - good, converter pressure FAILED. So per manual removed pump and checked converter relief and blew radiator line out. The manual doesn't really state what to do next, but my question is why does the converter pull strong when the tredle is depressed for a few? I've tried following the hydraulic flow chart and it really doesn't make sense. I also swapped out the two spool valve for another I have on a parts tractor with same results. What do you suppose the problem could be? Some seal in the converter multi disk piston?