Easy "Timed Stunt Driver" achievement
Become a level 4 skill driver and you will be able to jump and stick yourself to buildings. Find a tall building clear of street lamps and other things. Make sure you are away from the building slightly. Go slow, jump towards the building, and raise the nose of the car in the air. Press B again and stick yourself to the building. Drive up the wall. When it releases, you will fly backward slightly. At this moment hold Analog-stick Back for an easy backwards flip. Repeat this five more times for the achievement.
Go to the Easy Riders Garage in the Los Muertos territory by the lighthouse after you have secured it from enemy hands. Note: This was done with a skill level 4 Agency SUV. You will have a regular jump ramp an two barrel roll ramps. Start by using the regular jump ramp at speeds between 110 mph to 120 mph. Anything faster will result in you hitting the rafters; anything slower will result with the back bumper of your SUV landing and you will not get a full flip. Land it and continue around to the barrel roll ramps. Hit them at 80 mph to 90mph and land it. Repeat the process three times to earn the achievement.
Go to the beach in the Los Muertos area using the SUV on level 4. On the west side of the beach are two of the houses with ramps on both sides. You do not have to be very far or go over 60 mph to hit a back flip in combo with B.
Set up a co-op game with a partner. You must have the ability to pick up and throw cars. Take the Agency SUV (as you have greater aerial control) to an open area. Try the beach area north of the fairgrounds. Have one player stay in the SUV. Have the other player pick up the car and throw it (avoiding any rocks or structures). The car naturally tends to perform a right barrel roll. The player in the car need only ensure that the SUV lands on its wheels to earn the 1x Barrel Roll. Repeat this until you have done it six times in sixty seconds.