2-5 Seconds off the pace on most tracks? What's the biggest time savers?

Hey All,
New here. Just got my PS4 & G29. 

I've had F1 games in the past. And, used my brother's G29 on Project Cars with no assists (except lines for corners).

I'm improving all the time, but I'm finding on tracks that I've really put some time into, I'm still 3 seconds off the pace (if not more). Trying a few different ghost setups etc.

That puts me around the top 10-15% (again, only for tracks I've put time into). I was on point to get into the top 6-7% with an Australia lap time last night, but stuffed the last corner

I know there's still time to be saved, especially on tracks where I'm 4-5+ seconds off that I don't know 100% - but this just seems like a ridiculously big gap to bridge.

I can compete fairly easily in Expert AI, but when I go online multiplayer, the races with a Medium AI are full of people pulling lap times 2 seconds faster in most cases?

I didn't think I was that bad!!!

Without actually watching, what would you say are the biggest time savers. I'm trying to get setup for corners better to carry speed on the line and get a good exit, and that's helped, but I just can't see where I can be making 3-5 seconds a lap.

Thanks!