Yes, there are a number of modifications that you'll need to make to do this. The fan shroud, fuel filler neck & steering shaft will all have to be modified along with the linkages for the transmission, transfer case, clutch, throttle & tranny kickdown as well as extending brake lines & parts of the wiring harness (you may not have to modify all this stuff, particularly the stuff with cable linkages )
Sometimes you'll be able to get away without modifying this or that depending on the year of the truck, what options it has & how much of a lift you go with but the stuff I listed is pretty much the parts that are effected when you raise the body up & away from the chassis & drivetrain.
As Gatorbronco pointed out this is a question that's been asked & answered countless times and looking thru the archives will let you find the answers to a lot of questions like this without having to wait for responses to new posts. Don't get me wrong, I'm not trying to discourage you from asking questions, go nuts with it, just know that you can often find good answers in previous posts. Let us know how you make out.