Ok this problem with the transmission I guess is very common in the Impalas, I was lucky to have the opportunity to rack up almost 200k miles on mine before it happened but some people aren't that fortunate. The shaft from the transmission pump to the torque converter somehow pops a seal out which allows the shaft to start going oblong and eats the gears up, without the seal there the transmission fluid flows through heavier and builds up high pressure in the lines and makes the car slam into the next gear. So from what I was told I am just wandering how the hell does GM borrow so much damn money and still can't seem to fix a problem that has been brought to their attention I'm sure many of times.