i'm pretty good online, but not the best. sometimes i've been in races using the same car as my opponent, but it seems his car goes faster than mine, even when i think i'm driving good. i use auto transmission and i'm wondering if these people are using manual trans. to get an edge?
I'd think so. I switched to Manual for single player (Haven't played online yet), and I've cut -on average- 4-10 seconds off my lap times, with using a Works GT500. Manual trans makes a hell of an improvement if you can get good with using it; If you're bad a shifting, it'll probably hurt your times though.
Using manual trans also made a huge difference in my ability to navigate corners. After some practice, making use of engine braking can GREATLY improve both handling around corners, and the speed at which you exit the turn an re-accelerate (Which also saves lap times).