My Stratus 1996 transmission slips fron 2nd to 3rd

Hi, my car is a 1996 Dodge Stratus, 110000 miles, 2.4 l. My problem is that the trans slips between 2nd and 3rd gears. It has already been change the oil and filter, but the problem remains the same. Cut be the problem in some solenoid or do I have to do the complete rebuilt? Can I do something else? Thanks.