You need help diagnosing / troubleshooting the John Deere 4640 Powershift. After starting up, we need to wait a little while for the hydraulic pressure to build up for the three points, hydraulics, PTO and clutch / gearbox. Over the past year, things have gotten worse to the point where we need to crank up the engine speed to increase the pressure. Wondering which pump was causing this, I changed both filters / mesh to no avail. Have you heard there is a hex shaft drain pump in the back that sends oil to the front pump?
Your John Deere 4640 power / shift has a gearbox. Pump the back of the flywheel, no hex shaft, check the oil pan mesh and of course the trans. Filters, if he’s okay, then he’s most likely in a weak trance. Pump, check total trans pressure first, but it’s probably a weak pump.