I've a 2006 SS Impala. The first 4T65E trans failed just after the GM warranty period! Of course!!! It cost me $3200.00 to replace it with a 'Factory Certified' ( from Star Chevrolet in Greensburg, PA ) rebuilt one. They told me there were no 'new' ones. BS! (FYI Do not take your car there!)
Anyway, a couple of weeks after the replacement was installed... it started slipping between 1st and 2nd, and 3rd and 4th. It would slip... then SLAM into gear. Took it back to the shop (Star Chevrolet in Greensburg, PA) and left it there for a week ( and I know I shouldn't have ) where they put over 60...
60 miles on my car, and told me nothing was wrong with it.
I don't have to say, I WAS PISSED! As I pulled out of their parking lot, of course, the transmission slipped going into 2nd and then slammed into gear!
The little shop where I have general maintenance done on my car told me to put half a bottle of 'Lucas Transmission Fix' in it, and that it was amazing stuff. I did.
After driving the car several times after adding the Lucas, the slippage happened less and less. It stopped slipping completely after about 2 weeks and hasn't shifted weird since. In fact, I believe the transmission actually shifts smoother and faster than before.
I agree with my local mechanic. I love the 'Lucas Transmission Fix'! It worked!
(I do not work for Lucas, by the way.)