Well my internet connection has been down for a couple of weeks so I am back online and have just read the last reply. I don`t know about a switch for locking up the torque converter. Some of the other guys may know. After flushing and adding the lucas additive, the truck did well for a while, however, on occasion I am having the transmission bump again. Mostly when I have dropped speed below 45 and begin to accelerate again. The transmission shifts as smooth as it did when I first bought it. The flush and fluid change did make an improvement. Is there any other possiblites for this bumping?