Can someone tell me if replaceing the air filter with the K&N type filter and a megaflow type muffler is really worth the cost ie: more notable HP and fuel mileage? I have a 04 dodge cummins (auto)305/555 and tow a 13000# 5th wheel mainley in the sierra nevada and cascade mt. ranges. . I can hold 50mph going up these mts. but as everyone knows that you can't get enough HP or booze. Thanks for your responses. . Bill