I wouldn't waste too much money doing things that "might work" I would just check the fluid level and if it is full then look at finding a low milage transmission or have it rebuilt. At 106,000 miles I would find another one instead of rebuilding, especially if its the cheaper route. And if the guy drained and filled it, most likely it needs to be replaced. $1500 is a pretty good price for a transmission with only 6,000 miles on it. Hell thats how much the transmission for my old Bronco II was.