I took 2500 to the emission testing station to be tested and on the way home it had some difficulties shifting into overdrive. It has only shifted it to OD one more time since then. Could the emmission test machine have caused this or is it just a coincidence? It has an 8L V-10 so gets bad enough mileage with the OD working, it's downright scary without!

What can I do to diagnose the problem? My parts store manual doesn't even mention an overdrive, is there an on-line manual or troubleshooting guide? Any help at all would be appreciated!