Well I have an idea about the Car Missions.
1st: Currently, when you get a mission, you do not take any damage for like 20 seconds. But that's not long enough. Should be like that till you complete your mission.
But what if some players abuse it? There should be an timer, of around 1: 30 seconds till you complete your mission. That's enough time. The distances between locations aren't that big. I don't take more than 1 minute from the East Post Office to the Ammo Shop, which is the biggest ''itinerary''.
This is my idea from preveting you to waste your gas.
2nd: Some NPCs request you to pick up the doctor/hitman at the Southridge Hospital. And you have to be extremely accurate to get the guy spawned. Fix that please.
3rd: Players should have a fuel gauge showing how much fuel they have on their tanks everytime they enter their cars.