2004 efi is the 5l-e engine and can therefore be chipped. Easiest way to check is that if there is no throttle cable running over the top of the engine them it is electronically injected.
A few chips to that are available are DP Chip, RAPID and Red Dirt Diesel are the ones that I know of. I'm running a Red Dirt Diesel chip in my 5LE and I've had no issues. I'm also running an aftermarket DTS turbo kit.