Do you know whats wrong with second gear on myDewalt DC925-xe 18v cordless?

The drill is only three months old and the second gear on the speed selection will not stay in gear, it slips out in between second and third gear, when ever you try to drill something. The drill still spins when theres no force but as soon as you drill the chuck spins very slowly and makes a grinding noise. Do you have any idea whats going wrong and what parts i will need to fix it. Also should i relace any seals while i am there?Thankyou