Try cleaning the throttle body and IAC valve. I've had this as a persistent problem on my SVT. Your idle will run high (1200-1500RPMs) and when you shift, the revs will climb to 3-4K RPMs (or more) and hang there for a good long while before settling to a high idle. Instructions are
here for cleaning the IAC valve (major PITA - word of advice - remove the bottom bolt first). Some people say they clean their TB every 5-10K miles. Give it a try and good luck.
