All shifts, or only some shifts?? From standstill? After changing oil and filter without solving the problem you can adjust the modulating pressure on the side of the box, this will affect all gears and take off. If it is just 2-3 upshift, a spring kit has been known to resolve the issue in mine at least on a 722.503 box, kit no A1262704477. I think it will work for a 4 speed Cabbie box too.