Usually there will be some carbon or other debris in the schrader valve of the tester not letting the compression build. Also, all of the plugs should have been removed with the throttle blades blocked wide open. A six volt system cranks real slow so adding a battery charger to it will help get accurate readings. My experience thinks that 75 lbs. per cylinder or less will cause a misfire, so being in the 50's or less, the truck wouldn't even start. As long as it runs well and doesn't burn oil, let the sleeping dog lay,
Scott
