sprocket gearing change

I own a 2008 te 450 I'm looking to get a more highway friendly rpm out of the engine, I don't know much about the stock gearing or what I would have to do to achieve this if even possible. Any insight to the following would be greatly appreciated. At this point 55 mph turns around 4500 or more rpms. I'm not sure how long the engine would last at that rate or even if the motor can handle it. I do love my first gears single track ability but I still would like to see the rpms drop even if it means changing out my sprocket everytime I get to the trail. Thx

I take it back 50 MPH turns 5400 RPM on acceleration

I would start with increasing the counter shaft sprocket from a 13 to a 14, it is the cheapest way to try and will make a difference.

Top speed results today, after some very scary single track...

93 MPH, fuel cut off. fun in the sun..