Thanks again to all who helped get me running again this week when my van wouldn't start in Denver.

I'm back to Texas and she ran great the whole way.  After sitting about 10 or 12 hours today she is now only running on 3 cylinders.  The driver's side back cylinder is not running.  The plug is sparking and new and there is compression although I don't actually have a tool to test it by.  The plug doesn't seem wet even after it's been running.  The other cylinder on that side definitely gets gas and runs.

I'm thinking it could be a fuel injector.  Should I just put some B12 in the gas tank and drive around for a bit to see if it clears up?

TIA,
dylan