Sounds to me like you're just driving harder now that you're used to the SC. The SC adds power and the only way you add power is with more air and fuel. Every time you use boost, your truck is consuming more fuel than stock, sometimes significantly more.

This is exactly why the shift to smaller displacement motors with a turbo(s) to improve fuel economy is a bit of a farce. The smaller engines make the vehicles slower and laggy off boost, but MPGs are better than a bigger displacement naturally aspirated motor. When you dig into the throttle and get boost, the acceleration is much better, but MPGs plummet severely. For some applications like trucks, the motor is under boost almost all the time and often times will see worse MPGs. The V6 TT Ecoboost Ford F150s are prime examples. MPGs are actually worse than the much less complicated naturally aspirated and far more reliable 5.0 V8. And that 5.0 isn't much slower and sounds far better.

There's no free lunch here with boost.