i have no hatered for body lifts. that said i wont go more than 2" on my own truck. i think the biggest problem would be the steering shaft. Are the brake lines coiled up by the master like the older trucks? if so they will most likely be fine.might want to make sure there is slack in any harnes that goes down to the frame. your bumpers will look gay if you dont bring them up with the body IMHO. just take a look along the between the body and frame think will that streach 3 inches.
body lifts make trany removal a lot easier because you can then kinda reach the belhousing bolts.