I installed both, but I had someone paint the spoiler for me. The rear diffuser is not too hard - there is a line on the backside of the bumper cover that shows you where to cut for the diffuser and the instructions that come with the factory part are pretty good. Drilling for the spoiler is a bit more difficult. You need to have the right drill bits & hole saw as well as some good rust sealant paint. Directions that come with the factory part are fairly straight forward and include a nice template, but it's pucker time when it comes to actually putting the drill bit onto unblemished trunk lid!
You could probably get American Body Works in Lewisville to install for you.
http://www.americanbody-works.com