No offense taken from those who do not favor GM. I've gone through about 3 trannies now in this car but it's really my fault for a couple of reasons. First, the way I drive. I'm on it all the time and love burnin' rubber on the streets. The second reason is because of the buildup of the trans, in particular, the Stage 3+ shift kit. The builder knew I wanted slam bang shifts and instead of adding the 3 washers in the shift kit to achieve this, he instead knew of a TF727 spring that would do the trick even harder. So, as a result my bangin' shifts, though tons of fun, just pounded the trans. One time I grenaded the sun shell so I upgraded that to a reinforced one. The trans is also the reason I've gone through 4 rears too, LOL. The stock rear (7.625") was made for the 265 V8 that came with the car, not the 350 that came in the Impala SS and 350-equipped Caprices (8.5"). Now that I have a stud girdle, it holds up.
The 4L60E is a weak point with any LT1/LS1/LS2 equipped vehicle, as it cannot hold up to the massive torque. Any GM guy worth his salt will tell you that. Some just put in a TH400 and are done with it for good, those take a pounding.
Here's an example of the good 1-2 shift in the Caprice:
1-2 shift
And a standing still burnout in front of the Ford dealership:
1-2-3 shifts, listen