550 tranny problems

[tdkreg]

We are having tranny problems with our JD550 dozer.
The forward movement is erratic. Working just fine for awhile and then no forward power. Reverse is strong and snaps in immediately. Forward will creep along until the blade hits something. Shifting up and down through 1st, 2nd, and 3rd, you can hear the tranny changing. About 5 years ago the reverse clutch pack was replaced and the forwards looked fine. If this is a filter or screen problem reverse shouldn't work either? There is no pattern that makes it stop working...it does it cold or hot, it will work strong for 5, 10, 15 minutes, then quit. It might not start working for a long time or come back in a few minutes. We took the floorboard off and checked the linkage and all seems well there. The dozer is out in the woods now and we won't be able to get it to the shop for awhile, so testing the pressure is hard to do now.
Any ideas, suggestions, remedies?
Tim

[digitup2]

Check your pick up screen and the middle of no where isn't the greatest place to do that you have to empty the trany to get to the screen .just don't run a machine long that the oil pump is starving or cavatating for oil it is a good way to get into a big big mess!.Digitup.