Turn around then head back along the highway towards the garage. You'll need a wide turning area because you can't reverse very well at all with a gas tank attached to the back. So get in, and drive the truck all of the way to the end of the highway. He'll stop the truck a short way down the road and tell you to get in. Cesar will then jump from the bike onto the truck and jack it. You need to drive to the left side of this tanker and hold in position next to the door. You'll see a petrol tanker which is driving along happily. Drive the bike across the Kincaid rail bridge and get onto the highway.
When the mission starts, get on the bike with Cesar. He says you'll need a friend to help you out, so Cesar has come over. He needs you to do jobs which he can't be caught doing. Toreno explains who he is and what he's here for.
