A few years ago I had a problem that looked similar to yours but not quite as bad. During the 2018 season I noticed my 2-3 shift was spongy feeling. I continued to race like this for a few more events before removing the trans and inspecting it. Upon removal the converter did not slide out easily but I had to tug on it a bit to free it. The internals, bushings, thrusts, high clutches were discolored such as yours but not as bad. The pump had one drive lug broken off on the small rotor and while inspecting the housing, the broken piece fell out of one of the passages. I cleaned and reassembled the pump using A&A heavy duty rotors, Cleaned the thrusts and bushings, installed new high clutches and steels. Ran it thru the whole 2019 season trouble free and shifting hard and strong. Removed and inspected it during the winter and everything looks perfect. I can only relay my own experience with the broken pump lug. Can't really say why the pressure was lower but I do believe the broken drive lug caused it.