Couple of things I was wondering about were year model, chassis style, mileage, and maintenance. If you look at Pinpoint test "M", the first step is to clear the codes and retest, if no codes return then the problem is "elsewhere".
The fact that you had to drive the vehicle to get the code to return indicates you are most likely dealing with a mechanical fault and not an electrical issue. P0087 has always been a low pressure supply issue in my dealings with these things. To properly rule out low pressure, the truck must be driven hard and under wide open throttle. I am willing to bet that the pressure will be under spec.