I drive around in 3rd gear when I'm running a tank of gas that has Seafoam in it. I like to make sure I get the RPMs way up to thoroughly clean everything. Terrible for gas though. Even worse on my 5.3.
But reading the first post, it sounds like @OP is just feeling the responsiveness that comes with being in a much lower gear than you need. Like when you put a manual in 3rd on the highway. You're wasting tons of gas but if you just look at the gas pedal, see ya later!