If I had your engine doing 30+ miles per gallon in combined city/highway milage the last thing I would do is shake up the crud in the injection pump with a purge. I assume it is the 617 engine you are reffering to. It might truly be a case of if not broken break it. I have noticed the better pump rebuilders do not like this stuff and their explanation makes sense. You are simply probably getting the best fuel milage and performance this design is capable of right now. Others could duplicate it if they learnt to tune their engines with a system. They seem to like lower power than you have and poorer fuel milage as well. I want and seek all that is safely there myself. I do not suspect you have even one marginal injector but if you wanted to test for one it can or all of the injectors be tested in the engine quite easily at no cost other than a little time and a set of heat shields. That of course only is required if another simple preliminary test indicates the test is required. I guess the only thing I would think to recommend is to change out you fuel filter at factory specified intervals unless your area is noted for dirty fuel.