My 2013 3.6 always had a bit of low end slippage. I bought it with 75,000 km (@47,000 miles) and didn't really notice it until I started trying to see if I could burn 4 wheel rubber LOL. Mine is different in that it is worse the more it heats up. And it is mainly 1st gear, once I am in second I can floor it with no issue. I had the fluid changed a couple times with no improvement.
However, the good news is that it has not gotten worse and I now have 213,000 miles (@ 342,000 KM) on it and it really isn't much different. At this point it's not worth a tranny rebuild as it has practically no trade in value due to the high mileage. I'll keep driving it as long as I have confidence in it. It has truly been an amazing car, I just took it to Florida averaging @ 23MPG while cruising between 75 and 90MPH most of the way.
While totally different issue than yours, my suggestion would be to start with getting the tranny serviced and hope for the best. I don't recall hearing a lot of bitching about the trans one here, they seem very solid overall. good luck, I hope yours outlasts mine!