Same exact problem.........
I had this happen to me I pulled over one morning and checked it out. I opened the Hood and a 750 lbs Tiger jumped out and took down a neighbor kid on the way to school. I guess it crawled up there to get warm. What a way to start your day.
Seriously, I had this issue with my 454 Sub when it was hot. I am glad I saw it here as I plan to move to Alaska and I will have this most days now I won,t freak out and take the Casull to it. http://www.fishandhunttexas.com/454casull.htm
I did the Banks Monster Exhaust, Banks Intake and Super chip programmer. I noticed the Beast is very quite now.