Preserving transmission synchros

Cvzg77r

I have a 12 with about 56k miles on it and I had my transmission replaced twice, one for 5th gear and the other for 6th gear. The first time I fought with shop foreman the second time they just put it in there. I'm a senior tech (at lexus so noises bug me a lot) and I was not about to have him tell me its normal lol it happened in 10k-12k mile intervals If i remember right the first one was around 12k and the next one around 22k. I drive the same as I have then and the third transmission has been fine, and recently I've experienced random sticking csc and clutch slippage issues (after shifting to second at times the pedal doesn't come up all the way like as if it looses pressure and the rpms just go to red line and burnt clutch smell comes right after and the pedal is very soft and then it regains pressure. They already bled it and put in gtr fluid as if it would magically solve everything.) Also the way I found my synchros failing was either shifting from 5th to 6th and 6th to 5th.