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Someone correct me if I am wrong, but the general rule with slush boxes is that there is more slippage occuring with "smoother" shifting. Slippage results in more heat being generated and heat is one of the biggest enemies to automatic transmissions. And yes, a shift kit will generally tighten up the shifts.
The last time I installed a shift kit on a slushbox was in 1998. It was a chebbie with a 4L60E. I used a kit made by B&M. It was a pretty straight forward install. Check out BMracing.com