looking into a rough country 2.5"leveling kit with the 1.5" rear block lift and rear shocks, but i also want to stiffen the rear springs up? my question is does the rear lift portion rule out a timbren kit or air bags?i dont have a problem with hellwig helper springs it just seems the timbren are the least expensive. any help or thoughts would be appreciated. also should i replace the front shocks too, truckhas 28,000 miles