Took out the truck today (1999 Sierra with the 5.3) punched it from a stop and heard sort of a grinding/crunching when going from gear to gear at high rpms. Did the same thing in the 123 selectable gears. Still pulled extremely hard will no slippage, transmission was flushed last year and has around 200000km on it. Daily driving it drives good, only when in high rpms does it make noise. I was thinking maybe torque converter? anyone have similar experience? Any ideas to if it’ll be a cheap fix or need entire rebuild?