? concerning a 2000 dodge durango trany problem?

recently purchased a 2000 dodge duranago slt . we have been having problems with gear shift. you have to slam the gear shift into park or it will not start up after u shut it off. also at times when you put it in reverse it acts like you are in netrual. the dealer says this is normal but i think he is full of it. anyone else have this problem and how was it corrected thanks for the help