Balancing an engine

Heres one for you all, the engine shop I had my stroker built at: Baril Engine, had a project they did for Schnieder Trucking, (big orange tractor and trailers) and maybe some of you know how big they are, anyway, the idea was to tear down an engine and balance it and see IF it got better mileage, well the diesels were getting approx 4-5 mpg before the balance and they got 6 to 7 AFTER the balancing, that might not seem like much but when some of these trucks go over a million miles that is HUGE, so what did Schnieder do?? well they did it to 10 of their fleet then quit, don't know why but thats big business. Not really answering the op's question but I thought I would give my .02