Does it chug for a few seconds then release??? If so, I believe it could be a bad coil pack, your spark plug firing order is ( 1 - 4 - 2 - 5 - 3 - 6 )
The engine cylinders are 1 , 2 , 3 from front to rear on the passenger side of the engine and 4 , 5 , 6 from front to rear on the drivers side of the engine The coil pack towers are numbered 1 , 2 , 3 from front to rear in the row nearest the passenger side and 5 , 6 , 4 from front to rear in the row nearest the drivers side.
Here is a simple test for you to do. Remove the plugs t cylinders #2 and #4 and attatch the plug wires to them and touch the plugs to ground and start or crank the truck. See if you get spark from the plugs. If you get no spark, you may have a bad coil pack. They are know to fail.