Think Big (1989)

A teen genius (Ari Meyers) escapes from a teen think tank with the plans for a secret weapon. On the run, she stows aboard a truck driven by two slow-witted brothers (Peter and David Paul) who are transporting toxic waste across the country. Martin Mull also appears as the mentor of the think tank, Claudia Christian is the school's psychologist, and David Carradine is a repo man.