this is an issue that comes everyso often with my 05 SS 5.7 when i take off from the lights it takes it auto to register 'ohh lets go' its only like 4 seconds for it to shift
it has a tow pack on it
i know the 4 speed is a tough bit of gear only to be broken by the GTS 300kw monster
Get a shift kit and move ur shift points. Iv got a stage 2.5 in my v6 wags and it goes great one of best mods iv done