Keys are BS for that much lift, can't be done. I assure you. Do yourself the favor and maintain the truck and save for a lift. What ever it is you wanted to buy will make the truck ride horrible and or be unsafe. Do this right, please. Lifting is not cheap/ end of story. The kit is a grand plus odds and ends, plan on at least double that and that does not include tires, wheels, gears and so on.
Feel free to try cranking your stockers, they would give 1-2" and put a block out back to add 2"