It is fairly common with the 4.6 to have a hanging idle. They were programmed with quite a bit of airflow between shifts and even when at idle while moving. While it is common, there are a couple things you can do to tame it. Some IAC valves are worse about a high idle than others. If you aren't using a motorcraft IAC, replacing the IAC with a motorcraft/factory valve can help. You can also program around the issue using a tuner or having someone that knows what they are doing tune your car. The typical functions with an effect on the IAC are related to the idle dashpot and there are multiple functions and values that can be changed to affect the performance. Another option is the IAC mod. this is basically a modification which places a restrictor inline with the IAC valve. This reduces the maximum airflow the IAC can move, and thus reduces the hanging idle issue.
Its not a clutch issue for sure.I watched it closer today and it jumps up about 200 rpm's as soon as my clutch releases off the flywheel during upshifts but comes down perfect while downshifting.
google it. its really not difficult, you can make one using a pop can and scissors if you want. all it really does is restrict the amount of air the iac can move through the plenum, which will get rid of your hanging idle problem and make the rpms drop much quicker after your rev it.