Well, for starters, the truck model is very, very rare. It’s an older Jeep J series pick-up, sometimes called the ”Gladiator”, and it was produced between 1963 and 1987. The transportation coordinator found one in the making of Tremors 1, and the truck was used trough the movie (until a Graboid ate it’s tires).
It wasn’t so easy finding another for Tremors 2. When the producers were unable to find a whole working truck, they decided to build two from the parts of three trucks! This may sound complicated, but it’s actually very simple. Usually the film makers have at least two copies of every important object appearing in the movie, such as cars. In Tremors 2, they used two trucks which they had pieced together from three other trucks found in junk yards. Which truck they used depended on the type of shot they were filming. Better still, if something went wrong with one the trucks they could keep filming with the others. If you watch closely, you can spot the differences.
This information was kindly wrote for the Official UK Tremors site by Samuli Suominen from Finland, who also sent these pictures of Trucks of the same model number. They are slightly different in design but the grill on the front stands out uniquely.
Earl isn't going to be in Tremors 3, but let's hope his ace truck is!