That is NOT normal dude. Rail hang is very common. Like D45 said, it's excess rail pressure that cannot be bled off fast enough when you let out on the skinny pedal. I truck when it was stock would NEVER have any rail hang. Now that I have added my mods and added more rail pressure, it will hang a little bit when I really get on it, but only if I push the clutch before I totally release the skinny pedal. If I release the pedal, then push the clutch, there is no rail hang. It can be annoying, and I only have it when I have my programmer cranked ALL the way up, but a stock truck should not be doing that. I am guessing that there is either a tune left in the ECM, or perhaps the return check valve on top of the fuel rail is faulty causing it not to bleed off or return fast enough. That would be my first guess.... I had a buddy who was hot roding one day, and he turned his pressure way too high. He pushed in the clutch too soon and suffered from PTV problems. Not a good thing on stock valve springs if it is severe.