I served 6 years in the PA National Guard as a 91J, I am re-enlisting as a 19D will I have to redo BCT since it is OSUT?

Probable. But, the only ones to really answer that one will be MEPS and your Recruiter.

I THINK there are reserve component schoolhouses that do an MOS-T (prior service) 19D school. Might even be at FTIG. It’s been a while since I was in the schools realm though.

Depending on what they say there's basically two routes.

1. You'll insert into AIT at Benning and complete 14 weeks of training.

2. They make you go back to Basic and go through the whole 23 week OSUT.

3. They send you prior service basic at Leonard Wood (~5 weeks last i knew) and then go to AIT.

As others said, comes down to what HRC ultimately says as they typically handle prior service re-entries. Hit me up if you want to know more and what to expect.