A pump and garden hose at an average of 2 gallons per minute would take over 76 hours to fill the truck.
The best way to get a big explosion, though would not have the truck full of gas, mostly fumes. I've heard the fumes of 1 gallon of gasoline have the explosive power of 8 sticks of dynamite in the right air/fuel mixture.
Secondly.. a truck full of fumes is more LIKELY to explode, but a truck full of liquid will make a LOT bigger bang IF it explodes.