Where is my transmission dipstick located?

Here's that this transmission does not have a dipstick, rather a fill plug and a drain plug. You should have professional assistance in checking transmission fluid level for this vehicle. By the way, your concern about being stuck in third gear is not likely a fluid concern but something that will require some diagnostic testing by a professional anyway. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops