Everytime I take my 5.4 to get emissions, the computer is not ready. I have driven it over 300 miles, mostly on the highway. What else do I need to do to complete the drive cycle?

 

What are you doing before you go for the inspection? If you're doing any maintenance and removing the NEG battery post, then that will reset the PCM and you'll have to run it out for a while before it'll read the emissions correctly.
What state are in?