We first see John's Truck at the end of 1.16 Shadow. It is also seen in Dead Man's Blood and Salvation. The truck was last seen parked on the corner of Wabash and Lake, outside the warehouse in Lincoln, Nebraska where John went to meet Meg in Salvation.
The truck is a 1986 step-side GMC Sierra Grande. It's almost certainly an automatic and most likely a 4x4. (A definite 1986 GMC Sierra Grande for comparison.) It has a well-stocked weapon's compartment.
John's Truck has been nicknamed Truckzilla by fans.
When the truck used in production was being sold, it was described as:
"It is a 1981 GMC 4x4 short box step side.The motor is a 350,hp (strong running),auto trans. The suspension has a lift kit and has stainless exhaust. A new b&m shifter was installed and has tilt, sliding rear window and a cd player. There is a weapons stash under a false floor and is all automatic with a flick of a switch (there are no weapons included). The trans has a oil leak but works well." (Source)
Truckzilla was purchased in April 2008 by livejournal user blacklid. She outlines the experience of going to the set to pick up the truck in her post "Our trip to that Big Building in Vancouver What Has All Those Cars and Sets and Crew and Hockey Sticks and Whatnot, right?".
Truckzilla (now affectionately known as Zilla) made her first con appearance at the Salute to Supernatural Dallas 2008.