I'm Chris, Thanks for coming to Just Answer, I am going to do my very best to assist you with this concern in a timely matter. If there is any doubt or further explanation needed on my answer, just reply on this thread and I will get back with you. I am here to help you, so I want to make sure your satisfied.
Are you getting any warning lights on or flashing?
When it will not go into 4th does it just rev up when it gets to the top of 3rd gear or does it not even attempt to shift?