I have a 2000 GMC Sierra with a 4L60e that has over 200,000 miles and recently it has been acting funny. When I go to put it into D or OD it does not wat to go into gear unless I rev up the engine and of course it will bang into gear."Ouch" But if I pull it down to low and manual shift it throught the gears it will shift all gears. After I have manually shifted it through all the gears and I come back to a stop it will shift automatticly on its own with no need to manual shift. The first thing I did was to drop the pan and change oil and filter, but this did nothing to help the problem. The next thing I did was to hook up a pressure gauge to the main line pressure and at idle I am getting about 50-60psi and while driving I get from 90-110psi. Under hard throtle pressure the pressure climbs to about 175psi. Also when I first start the truck for about 2 seconds the pressure is about 75-80psi and then immediatly drops to the 50-60psi range. Can this be an EPC solinoid causing this problem?
possibly EPC solenoid. probably a worn pump or pressure regulator valve in the pump.
Those pressures are slightly low but you probably have lots of internal wear.Instead of wasting money trying to patch it up your better off getting a quality overhaul.