Hello, and welcome to the forum.
Please read the forum before posting. This is where spoiler questions are asked so that people don't accidentally run into them.
The answer to your question is on this
VIDEO #3. Make sure your engine is upgraded, and keep your foot on the gas
during the cut scene. You need to reach 80MPH fairly quickly, and the default engine on the original truck, or a low HP engine just won’t do it.