I did experience that so call 3-4 shudder with the 3.27 on the car. I would say that my tranny cooler and the fluid flush took care of 99% of that shudder symptoms.
My 4.10 came after the cooler and the flush and i never experienced any problems with down or up shift of the tranny. I would even say that when i let off of the gas while in 3th gear, the car down shif real easy and it even looks like a 5s tranny manually downshifted.
Im using the crappy hypertech and i did lowered all my shift point by 500rpm except the 3 to 4 shift. That probably help about the hanging in gear before upshifting
I think there s a TSB on the tranny shudder. Only way to get rid of it is fluid flush, tranny cooler and appropriate oil.
Just my 0.2