Why would a '98 GMC Safari or Astro V6 run very rough at idle and make growling noises but not while driving?
Astros and Safaris often have a problem with plugged fuel jets. Once it's running the flow is better but the problem while idling is not solved. GM makes a fuel treatment product that works well to prevent the plugged fuel jet (recommended once a year)and it could help to use the treatment now. It could be your motor mounts and transmission mount are worn out. We had the same problem and we were told it could be the transmission, fuel system, etc. The dealer wanted over $500 to repair it. We got all three mounts at Auto Zone for $60 and my husband fixed it in an afternoon.