Alysraza

This happen for almost all engines when you use infinite fuel. If you want to go with infinite fuel, cut off your engine instead of throttle, you shouldn't experiencing any framerate loss.

Lots of games are much more resource consumer and are really smooth, the problem come from the engine used by the game not the console. Yes optimise code is probably the best way to improve framerate without changing the game engine.

If you turn "Hack Gravity" On, you're good to start a new game. (All saves from that game are affected). The only way I found to get stock gravity back was to start a new fresh game.