I can't give a definitive answer, but I had a cap designed for a 73 and up Chevy. It worked, but did not fit well. It was about 1" too wide on each side. I think that would be a killer on a tonneau. The Extang BlackMax for your truck is $253.65 here with free shipping
http://www.autoaccessoriesgarage.com...-Tonneau-Cover, and you may be able to get a 15% discount if you call. You may be able to do better if you look around.
EDIT: Hmmm... looks like you just got similar info twice.