My 2Cents: Take the old ones off and measure, then go buy some new shocks. I bought my from Pete and Jakes:
http://www.peteandjakes.com/parts/parts_dept/irod.htm
You might also look at:
http://www.jcwhitney.com/Truck-Performance-Truck-Shock-Absorbers/600015560.jcw


~Jim