"Kits" intended for lifting purposes in a four wheel drive, are just that.
BUT some manufacturers put anywhere from the minimum parts required to do the job, all the way up to including brake hoses and relocation brackets, rear brake proportioning valve brackets.
It all depends on the vehicle, the manufacturer of the kit, and the price.
Your truck should only need what the kit included for such a small lift.
After 4 inches most lift kit manufacturers either recommend relocating the brake line flex hose brackets, or replacing with longer hoses.
A 3 inch kit shouldn't need much done to the steering, shock travel, or anything else, if its a good kit it will include this information in the instruction/warnings paperwork.
My boss at work just installed a 3 inch kit on his 96 Cherokee, and it only needed the parts included in the kit I helped him pick out, front coils, and rear add-a-leafs, and the rear through bolts.