Pulled/reinstalled slant6-won’t shift out of 1st now

Sounds like your shifter is out of adjustment. You might actually be in second not drive, thus why it rolled when you thought it was in park and having to push the gas halfway to get it to move. That would also explain why it wouldn't shift. If it was out enough you could actually be in first, not drive, and be shifting up to neutral, not park. Something could've got knocked out of wack without you noticing during the bushing change