I maybe able to add to this. I am a former owner of a VX (and will be again in the near future as $550/month wasn't doing it for me )

I now drive an 81 Olds Cutlas with 30K original miles (bought it with 17k)

NOW, over the past 18months I've also noticed that I am getting like 15MPG and this is after 3 tune ups.

I decided to do a little investigating. Has anyone ever thought that the gas stations are WATERING DOWN THEIR GAS???!?!?!?!?!?!

I can ONLY drive my car on 93 octane and anything lower causes EXTREME ENGINE PING. This has only started to happen and is MUCH MORE NOTICEABLE in a carborated engine.

I asked the dude over at the local Valvoline and he didn't DENY this is happening, just isn't in a position to start pointing fingers.

(ps. STOP HATING ON THAT VX. There are plenty of us out there that would LOVE to be back in theirs )