I own a 04 4.6 with Efans....when driving my temp Needel stays normal temp but when I get stuck in traffic...it begins to to overheat. Coolant is full and I hear fans kicking on but still will creep to "H". I'm stumped on this..

 

^^ I do smell the smell of coolant when walking in front of truck so I'm sure I have a leak but no spots on ground and overflow tank stays full for a good while but slowlys drops in the overflow tank but nothing crazy fast