Will I need to regear my truck after installing the lift kit?

Short answer, No. From the factory your vehicle is tuned and calibrated based on optimal axle ratio for the original tire size. If you lift your vehicle, install taller tires that original ratio isn’t ideal and may result in more sluggish acceleration/performance, transmission shift points being off and more strain on the powertrain. To what degree will depend on the change from stock to lifted tire size, your intended use for the vehicle (highway, offroad, towing, etc) and in many cases the original gear ratio is “good enough” to live with. So can your truck drive on 35”, 37” or even 40” tires with stock gears, absolutely, it’ll just be a bit slower. There are several programmers on the market to help adjust shift points as well as tune to regain the perceived loss in engine performance caused by trying to turn the larger wheel/tire mass.