extremely soft 2nd to 3rd shift

And yes, these guys that did my transmission think that they can do no wrong and that they know everything, the owner likes to argue with me over every issue i have had to bring it to them for.
First one being that they put the wrong torque converter on my engine and then tried blaming the vibration i was getting from it on my engine not firing on all 8 cylinders lol, Then i proved to him that it was running on all 8 cylinders so then he blamed it on my rear axle, I dis proved that by putting the transfer case in nuetral and running the transmission thru the gears and the vibration was right there, At that point he finally agreed that it very well could be the transmission causing the vibration.
So i like to do re-search on issues before going to him so that i can have some facts to back up what i think is happening because he loves to argue with me, i dont think they like doing warranty work.