I have a 99 Astro as well.
The problems that you talk about showed up on mine around the same mileage.
The rough running/jerking started first and then the cold/wet start problems.
On mine the problem was the coil.
It was shorting out to the bracket.
When it was cold and wet and it wouldn't start you could actually see it arcing to the bracket.
A replacement coil from Autozone or Murrays is around $35.
It isn't the easiest thing to change though, but doable if your paitent.
It sits up on top of the passenger side of the engine. near the throttle body.
Good Luck
Mark