D5C Hystat Overspeed Valve and Rear Speed Sensing Valve?

D5C Hystat 5HS00484- Just had the rear hystat travel pump rebuilt ( leaking). The machine moved and operated just fine with good test pressures before shutting down and removing the rear travel pump. After reinstalling- I now have faulty test pressures at the overspeed valve ( mounted just under to the left of the foot brake pedal). At idle 800 rpm, the test port pressure on the overspeed valve is suppose to be 230 psi, and the signal pressure should be 145 psi. What I am seeing - when I start the machine I instantly see 145psi signal pressure then it instantly drops down to 50 psi- the overspeed test port pressure is 400 psi. I have read the hystat testing procedures-and it says that if the overspeed test port pressure is too high , it should be decreased by adjusting the rear speed sensing valve-- I did this- but NO change. still reads 400 psi----- If I disconnect and block off the hose supplying oil to the overspeed valve - then the signal pressure stays at 145 like it is suppose to, and the machine will now move and function as normal. Any ideas as to what is wrong? The only changes to the machine was rebuilding the rear hystat pump. The shop that rebuilt the pump said maybe the rear speed sensing valve is stuck open? ( it was working fine before and all they did was clean it and reinstall- they said they did not adjust it) Also, this overspeed valve sees oil pressure from 2 input sources - a supply line on it's left side ( the one I blocked off), and is T'd into the signal pressure line on its right side. Not sure exactly what the overspeed valve does? - does it have some sort of internal shuttle valve that regulates/modulates the oil entering it from these 2 sources? Any help/info / advice would be appreciated.