My 1999 JD 450H LT starts immediately and the ground speed is normal for 2-3 minutes, but then it slows to about 1/4 MPH no matter where the engine speed or transmission speed levers are positioned. The engine sounds the same after the ground speed drop-off. The transmission control unit reads "RUN". Any suggestions for the speed change?
I would suggest following the wire loom and looking for a place that may have rubbed and is causing a short that may cause the trans controller to think the slow speed is being requested. Most problems in these seem to come down to wiring issues, in my experience.
Thanks Jerry, I just hope it doesn't end up being the controller itself since it cost over $3k.
Did you find the cause of the problem? I might have something similar. The speed is stuck on 1.9 and will not go up or down.
Although I could not feel or hear any problem with the engine's performance, it was a very low fuel pressure. Pressure should have been 4lbs but was just barely moving the needle on a fuel pressure gauge attached to the line. I replaced both fuel filters and the problem was resolved.
Was going to be my first suggestion! Glad it's lined out!