Sorry I have not posted here is what I discovered so far. I got in touch with the dealer who sold the machine originally. They were still in business as a different dealer but had the record!!!!! By the numbers the machine was originally a Y 180.
The original machine had a telescopic lift cyl. This may explain the double lift pressure valve for high speed lift.
I removed the upper pressure line off the cyl which is now a single cyl, converted it to a return to tank and plugged the pressure line. The machine now cavitates on lift when lift is about 48" to 60" then it's fine. Perhaps the valve which is a double lift equalizes and cavitates or perhaps it's just still a bit airbound?
The cyl is leaking but I think the rebuilder did not do the top packing very well.