I actually had that same problem in my mitsubishi a couple of years back, I ended up changing the trans fluid and the filter and putting the car in OD mode off and that worked for a couple of months, but then I ended up getting stuck on the road oneday when it completely slipped. I ended up have to replace the entire tranny (that sucked) I hope its just your soleniod because its a lot cheaper. Let me know what the shop tells u