I would spend the time and money and go to an alignment shop w/ a machine. Get it set and take it straight home and duplicate the numbers. At least see what your equipment reads and compare to the digital rack numbers. Get a good reference point. Caster is one of the more "subjective" measurements. Its also what could be hurting you. 4 degrees sounds low. I run 4.7 or so. Less static camber ='s more caster needed.