2011 GT, I think the code is the culmination of an issue that's been underlying for a bit. Motor has been rebuilt, block prepped, stage 2 ported heads, stage 2 cams (vct locked out), 302 intake, JLT MAF, unk TB, Kooks long tubes, high flow cats. JLT catch cans on both sides with new PCV. Just replaced upstream b2 o2 sensor for previous CEL. I've suspected a vacuum leak because of "hanging revs" between shifts. However, idles smooth and didn't present with the usual leak symptoms. Figured it was just in the tune (unknown tuner, B&D in LA did the build) Sunday, after a strong 3rd gear pull to 7k to motor would no longer respond to anything more than half throttle. Raspy engine sound muted. Would still rev to 5k but at reduced engine power and noise. No codes. Very smooth running, just at reduced power. Yesterday, tried to data log (it didn't record) and the mild acceleration was noticably shuttery then CEL. P0174. On my to-do list. Propane vacuum leak test. Clean MAF (already cleaned tb). Record temps of both cats. Remove fuel pump and clean pick up screen. Likely causes of vac leaks? Chances the fuel pump has gone south (check valve not "checking", etc)?