My dad has a 06 G56 with about 36K on it. He has always thought that it shifted rough, nothing changed with the addition of amsoil ATF. He just chalked it up to being a HD tranny. His 2-3 shift is his worst, 2-N-3 is what he has to do, cold or warm... About a month ago he drove my NV5600 and said it was smoother than his G56, not a comment I hear often... We kinda shrugged it off.... Well this last week he had a loaner 05 3500 SRW while his was in the shop. He said the shift pattern was the same, but there was no way it was the same tranny as it didn't even shift similarly. The 05 he had on loan shifted like butter, no hesitation at all, he really thought it was a different model tranny...

So what can he do? Obviously something is wrong with his syncros, but what evidence can he use at the dealer?