I have a 04 4x4 1500 Hemi the cruise control only works to 55 mph after that it want hold and the cruise light want come on what do you think

 

Maybe check the speed sensor. Also, and it may sound dumb but it's true. Make sure your tires are the same size. For example if you had a flat and only replaced one tire the size difference can throw off the speed sensor. I'm not so sure about these trucks but my buddy had an f150 and he had the same problem. He did have a flat and only replaced one tire. Quit working, replaced the other three two weeks later with the same size and brand and all of the sudden it works again.