My 1999 Jeep Grand Cherokee 4.7 is only gettin about 12 mpg and it really sucks... As i'm driving it sounds almost like i'm sucking in air from somewhere other than where the airfilter is.. i just replaced my plugs and had to take off the air box assembly but now i'm actually getting less mpg than what i initially was.. and that is after a k&n replacement and new plugs...

Any Ideas?

I'd check for leak anywhere you can like around the pcv and items like that. My wife's jeep with a/c on gets about 20mpg and w/o it on around 22mpg and it is a 94 grand cherokee Rob

any new ideas on fuel efficiency?

I would take apart the work you did and check all connections, it's easy to forget something like a sensor you had to remove from a tube or the like.