This seems like a bit of an odd problem. A little history: After OD and transmission rebuilt an installed, a test drive gave sporadic results. Initially seemed fine but began dropping out of OD or not engaging at all. After a bit of analysis it was determined that the new switch was the culprit as it would not consistently work when testing. A new switch work every time. Feeling confident the problem was solved the interior was reinstalled. Test drove today. Again initially seemed fine, but then started acting up in 4th. Oddly, no problem was experienced in 3rd, but rather only in 4th. If in OD and going from 3rd to 4th it would drop out of OD. If not in OD and in 4th OD would not engage. Upon return I tested to see if I could hear the solenoid in both 3rd and 4th (car had sat for maybe 10 minutes). I could hear it actuate every time regardless of gear. Any thoughts? could it be a wiring issue with the isolator switch that only raises its ugly head with car in motion?