1999 Mazda 626 Transmission Slipping

This is going to sound like a wierd question but, I sort of inherited this problem. My wife got the car from her mom right before we got married. It had 91K on it and had just had the transmission rebuilt. At 94K the transmission is begining to slip badly again. I called the shop that did the transmission work or so I thought. Thay said they sent it out to a seperate transmission shop, which is now out of business, go figure. Apparently when the transmission failed the first time my mother-in-law was told that the CV joints she had replaced had been installed wrong and caused the transmission to go bad. My first question is, is that even possible? I need to know because the shop that sent the transmission out was the shop that did the CV joints. Second, I was told that they won't warranty the work on the transmission, because they sent it out. However they were paid for the transmission repair, shouldn't they warranty the work of their subcontractor so to speak?