"Follow Chop and search the boxcars for D" is an objective in the story mission Chop in Grand Theft Auto V
Walkthrough[edit]
As you make it into the train depot, start following Chop. He is on to D's scent. Hop on through the trains and take off after D.
After the next cutscene with D hopping on a train, you can switch over to Chop and use his perspective. Do so and run on toward the front of the moving train. You can search the first 2 cars, but D isn't in there. Switch to Chop and head past the train and over to the right. Look around the train depot to find a sweet lady dog. Just move on up on her for some good times.
Switch back to Franklin and pull Chop off the other dog. Chop will take off after D again. Go back to the train yard and open the first car door on the right. This will show D, finally. Franklin sends Chop after D to take him down. Just head on up to Chop and D to catch D finally.
