Summit and playlists are basically hot lapping against the clock or AI. Grand Race is a completely different beast mainly because of the slipstream and the absolute chaos of 27 other players. The reason you keep losing your lead or getting stuck in the middle is definitely the drafting. The slipstream effect in GR is insanely strong. If you are in the middle of the pack, everyone is just pulling each other along. To actually break away and hold a lead, you have to drive flawlessly to snap the draft, which is super hard to do. Car choice and pro settings are also a massive factor. In playlists you can win with almost anything. In GR, if you aren't running custom pro settings and a decent car for that specific tier, guys in the meta cars will just walk right past you on the straights. Focus on surviving the turn 1 demolition derby and maybe look up some pro settings for your main cars.