what would be the best size lift and size tires for my 2003 chevy 1500 i want at least to have 38 in tires  

wow   to clear 38s in a 1/2 ton chevy your gonna need at least an 8 inc lift and maybe some fender trimming and they should fit but really running 38s on a little 1500 chevy isn't gonna be good to your truck, the front ifs suspension is weak, your rear axle is also too small and weak to handle 38s offroad and your gonna need to regear your axles to offset the giant tires, at leat 4:88s gear ratio lower is recommended. if you use the truck mainly on the street it should be fine for awhile but your suspesion and axles just cant handle off road use