Not a GMT900 problem, but a tuning issue it appears.

 

i know my truck acts different depending upon what mph i floor it and it downshifts into first....sometimes it shifts smooth others its firmer.. sometimes it barks tires.. sometime it roasts tires sometimes it feels so bogged down it doesnt even chirp tires... its almost different every time.. i think it has to do with tq management on mine though.....