Gear Problem Of Kia Picanto

Dear Concerns: I have been using a Kia Picanto Car which is bought in early 2006 & run only 18500 km. But unfortunately I am facing problem with the Gear from the very beggining. In Driving mode in the Gear- the car is supposed to run slow or move automatically without Acceleration. But it works for Back Gear only, not for Front gear. Slight Acceleration is requited to put to move the car when the Car jupm unacceptedly, otherwise the Car stay without any moving even when the car is in Driving mode. Please advise on the same what I should do. I talked to Local KIA dealer from where the Car is bought, but they are saying to Change the Gear box at the cost of USD: 5,500.00 which is absert. Please help on my problem. THanks & regards Khurshed Alam