OK, you have cleaned the suction screen and return line filter. One note - the return line filter captures dirt internally. I think most people replace this filter, but did you clean it out internally? It also has a back-pressure valve attached to the end of it that should be checked for binding, excessive wear, or damage & replace o-rings.
Sounds like your pump is OK at 2500+ psi. Does the pressure drop when you raise the lift handle?
Do you have the lift in "position" control as opposed to "draft" control? I think the little lever should be in the "up" position. Won't work very well in the "draft" position.
Do you happen to have remote valves on your tractor? If so, is there a lift bypass valve on it? Lift won't work in bypass position.
From the troubleshooting section of my (Ford 3600) manual, here are some other things to check when lift is not working:
1) Flow control valve binding.
2) Check valve damaged or worn.
3) Draft control or position control damaged.
4) Unload valve or back pressure valve faulty.
5) Lift piston seals damaged.
6) Unload valve plug worn.
7) Lift cylinder, lift cover, or pressure transfer tube cracked.
Note that my manual is for a Ford 3600, so there may be some things that don't apply to your 3000.