Losing MPG on an 05 tundra!

How can i find out what is wrong with my truck?  I have a KN&N Cold air intake and a borla exhaust system.  I have cleaned my air intake every 10,000 miles and do the regular maintance every four to five thousand miles.  Do i have to clean my O2 sensors.  What else can i do?  I hope you guy can help me out.  

K&N air filter adds zero MPG on that truck. Anyone that tell you otherwise is BSing you. If anything it could slightly hurt MPG because will maybe cold air is best for WOT power, it is not best for part throttle cruising efficiency. On exhaust, this is another mistake if seeking best over all MPG. Your truck was well tuned from factory on intake and exhaust and you kinda threw that all out the window. Consider this, if it was that easy to improve MPG that truck would have come with duals because it would have raised its CAFA MPG results. It does not though because it hurts more than helps most of the time. It has to do with letting exhaust escape too quickly for cylinder at lower and middle RPM and less energy from it is captured and used. (expanding gases drive piston down not a explosion). One more thin, try using 89 or better octane fuel in it. 87 is a bit of a joke for that motor and only reason that it tolerates it is because it has active spark management (otherwise it would ping up a storm) Problem is while it is masking knock by retarding spark, MPG can take a dump. BTW, you will will never here it knock when active management is working properly.