4-6 hours? If you rush it, and take short cuts, and have a lift and all the right tools. Time also depends on how low you wanna go, what size rim/tire you want, to do it right you need a 4 link to really hit the side to side, if you mono leaf it (remove all other leafsprings except the main one you are gonna have mad wheel hop (4-link is the way to go keeps the pinion angle right at all times, no wheel hop). If you wanna lay frame on the tahoe you need to install a step notch or c-notch depending on how low you wanna go and you have to raise a section of the floor in the back so the axle has room. Also making room in engine bay for big rim tire combo, and an 03 tahoe probably has a lot of stuff over the fenderwells which needs to be relocated for clearance reasons. You need drop spindles or dropped tubular control arms to help keep corect camber when riding low. My guess on an 03 tahoe if you do it right 4-link,drop spindles,sectioning floor,relocating acc.,and notching the frame, a shop would take at least a week.