One thing my mechanic and I did to diagnose where the leak was coming from was to THOROUGHLY degrease the entire engine bay. Get a couple bottles of Purple Power and start spraying that thing down. Repeat the process like 3 or 4 times. Cover the entire engine bay with degreaser, hose it off (all when the motor is cold).
Then once it's clean enough you could eat off it, run the truck with that UV dye, and you'll see only the freshest leaks.