Toreno explains who he is and what he's here for. He needs you to do jobs which he can't be caught doing. The first one is to Hijack a truck. He says you'll need a friend to help you out, so Cesar has come over. When the mission starts, get on the bike with Cesar. Drive the bike across the Kincaid rail bridge and get onto the highway. You'll see a petrol tanker which is driving along happily. You need to drive to the left side of this tanker and hold in position next to the door. Cesar will then jump from the bike onto the truck and jack it. He'll stop the truck a short way down the road and tell you to get in. So get in, and drive the truck all of the way to the end of the highway. Turn around when you reach the grass. You'll need a wide turning area because you can't reverse very well at all with a gas tank attached to the back. Turn around then head back along the highway towards the garage. Go off one of the slip roads and head to the garage where you'll find a red circle to park in.
Mission Passed! $7,000
After the mission Toreno will tell you to get back to his place now. So head over there. He's known on the map as Toreno now, so head to the grey T.