If you are down shifting, there is a control feature that does not allow you to shift above a preset speed. This is a safety feature. I am not sure of the specific design set up, but I'm sure someone will be able to comment on that here. I would take it to my dealer if it is new and still within warranty. Also that particular model had 2 recalls. One for the clutch plate and one for tie rod ends. The dealer will repair these at no cost to you. The clutch plate might be your problem.