This topic has been beat to death several times here.
#1 there is either an open conter control valve, a closed Center control valve with the wrong plug or a blown O"ring. Or there is aRelief valve in the controls that is set below 2400psi.
#2 completely and totally sc3wed the pooch with the oil return direct to sump. It"s been discused here several times that the transmission pump is too small to supply the front pump. During high flow loads that drain the oil cooler and tank. Particularly a problem on older tractors such as yours with a worn pump and clutch or brake seals that are seeping with wear and hardening. Obtain the ported filter cover we are forever talking about and return the loader oil there. #3 oil supply to loader valves is 100% correct.