Normally, TSA doesn't care about how many carry-ons you have or their size. That is between you and the airline. They are the people that enforce the FAA 1+1 rule and size requirements. I often see airline personnel or contractors harassing people about those rules, not TSA. However, there is still a chance of running into a rogue TSO who insists on enforcing the rule as I did once in MDW when I had a slightly oversized bag that I was gate checking. The line at the counter stretched outside and down the sidewalk. I told him that it wasn't his job to enforce that rule and as long as the bag was free of prohibited items and fit into the xray machine it was allowed to go. When he insisted that he was right, I asked for his supervisor and showed my TSA ID. He backed down and I went through with no more problems and raced to my gate as my flight was boarding. I say give it a try and if a TSO hassles you, ask for a supervisor and be polite, but firm when explaining the issue to him.