They say for some reason, he crossed the center median of the highway, then rolled down an embankment and into oncoming traffic.
The pickup rolled into the path of a semi, which hit the pickup on the driver's side.
The crash happened just 200 feet south of the Tahoka city limits.
A Justice of the Peace pronounced Pennell dead at the scene about 10 minutes after the crash.
The driver of the semi, Joseph Martinez of San Antonio, was not injured.
The DPS is still investigating the crash.