6400 low hydraulic pressure

[russhog]

Here is my story. I have 6400 that would not move. i pulled the transmission pump the housing had some scaring. I replaced the housing, pump and all the valves in the pump. Now my tractor will move but i have to get the rpm's up to 1800 before it starts. The low pressure light will come on. Driving it across the field, it will pull down when i turn the pto on. It seems like a restriction. My filter screen is clean and the filters are new. Any ideas on what could be restricting it. I have a guage on the way to test the system pressure at the pump house. I also have a new main hydraulic pump and charge pump.

Any ideas would be appreciated.

Thanks