Jason, how did it affect your et and mph at the track? Most converter efficiency plots I've seen are pretty flat that far above the stall speed so the slippage should be approximately a constant number of rpm, so subtract that from the engine rpm and then multiply the remainder by the gear change ratio, then add back the slippage to get the final rpm. So if he is at 6400 rpm and has 400 rpm of slippage, than his rpm after the change would be 6400-400=6000, *3.23/3.42=5667, +400=6067 rpm, compared to just taking 6400*3.23/3.42=6044, so with 400 rpm slippage he would see 23 rpm less of a drop than expected. I guess you could compare the rpm drop on the 2-3 shift with the 3-4 shift to see if the slippage is different but my guess is that there isn't going to be much of a change in slippage with that load change that far over the stall speed.