I have an non-wheeled TUMI garment bag that I've used for carryon a number of times. The only time I had a problem was once on a CO flight from SNA. The gate agent got a bug up her behind and wasn't willing to let it on because it didn't fit the sizer (it was rather overpacked). I insisted it would fit in the overhead. Finally, she accompanied me on board, watched me place it in the overhead (it slid right in -- no stuffing necessary), and stopped hassling me.