I bought my '02 with 30k on it in Sept of '02. It had one of the "Good 'Ol Boys" farmer GN balls in the bed (under the bed is a 18" wide x 1" thick steel plate running frame rail to rail and welded in place). I know the truck was worked constantly, since the high beams were hitting lower than the low beams should when I turned the lights on. The only problems that I have had with the truck were self inflicted.
If I knew then what I know now about these trucks, I would still bought it.
Check the LP fuel pressure, check for codes, look at the color of the exhaust manifold and turbo. If the turbo is goldish, it has been a little too hot too many times. If the manifold is blue, same thing, and not a good thing.
Look at the suspension. Do the rear springs look saggy, heavy wear on the bump stops? Does the front of the truck sit level side to side? More than 3" from the control arm to the bump stop?
Have all of the fluids tested/analyzed before you buy (engine oil, diffs, transmission, coolant, PS pump... ).
Carfax report?