I had a problem with a Chevy truck that I had a while back. I would connect a hand scanner to it and not pull any codes, Took it to several mechanics and they couldn't pull codes. After a while I gave up and took it to the dealership. They connected there scanner and pulled 2 codes. I asked the guy why they pulled codes when no one else could. The guy (Long story shortened) told me that there are certain codes only the dealership could pull, He said it was because the fix for these codes regarded actually altering the ECU program. I don't know if that is the same situation, But I guess it is possible.

 

..try cleanin the tb first..I've seen limp modes on other hemis which cleared up after cleaning.... if not, it is a pcm issue..