Hi i have a 1998 gmc sierra z71 and it is verl doggy of the line and when you are going 105 km and put your foot right into it it kuts down and revs to over 4 thousand rpm and the battery ligh flashes and it then bucks and then almost sounds like it back fires and then up shifts

SOURCE: 1999 gmc sierra

Sounds like your torque converter is going out. If it is that when you go to shift the transmission is not getting enough fluid to keep the parts moving in the transmission. The clunks it the gears freeing up and smashing into the right position. I had a similiar thing happen to me with my old truck. That sounds like the problem you are having, but I could be wrong. I sure way to tell is to check you transmission fluid and see if brown or black. If its one of those the colors the transmission fluid is burnt up. Usually the trans fluid is red. Hope that helps.