I had the same problem, mine was running great, i changed my fuel filters to Jatonka spin-on filters and lost probably 20% of my power. i drive the same road everyday day and on one hill it would cruse up it at 50mph with power to spare, now it slows down to 40mph. what i did notice was that my primary filter was missing the gasket on the top of the filter eliment, it must have been bypassing the primary filter, so when i replaced all of them the power droped way off. i just ordered a pyrometer and boost guage today, so when i get them installed im gonna turn up the fuel.