It's not your imagination...some auto transmissions with the manual shift feature are faster to 60mph (and the 1/4 mile) when you let the transmission do the shifting. Mercedes' Tiptronic transmissions are like this. Why? I have no idea...I guess it's because when you let the transmission do the shifting, it knows exactly when to shift and does the shift more instantly, rather than waiting for you to give it the command to "upshift" and then it does it, creating a little delay in there. Plus, the transmission can probably manage the engine power better than you can. If you want to use the manual shift mode when you are racing (somebody or nobody), just make sure you take it to redline and shift immediately.