I've been messing with the vacuum system on my '85 wagon, so I can say that on these at least, no vacuum makes it shift hard while accelerating (upshift), vacuum makes it shift soft. I know it has the blue amplifier, however I've driven the other Western Slope member's wagon (83 I believe) and his also shifts hard with no vacuum on acceleration.

They also shift hard on deceleration (downshift) with no vacuum. I thought I ran over a big rock or something once, but no, a line had just come unplugged.

-Rog