450C Transmission Issues

[timberjack 450]

I bought a 94 450C dual arch and it takes forever to get the tranny pump to come up into the blue area. Sometimes it will rise up then fall back down. Once it is up and the skidder will move it is just fine and shifts strong. I am hoping it is the charging pump and not the torque converter. I changed the tranny fluid and cleaned the screen. Normal small amounts of metal on screen. No chunks. The guy that used to run it, said it was always like that. Depressing, it takes between 5 and 10 minutes after startup. Don't want to leave the skidder running all day.   

[ga jones]

Mine is like that in the cold. If I bring the rpms up it will come right up.