Thanks to all for the suggestions re my quandry. The actual one that worked was changing the spark plugs from Champian X A25's to Motorcraft F11. The car is a different animal. I didn't think the change would be so dramatic. The Champian plugs by the way were brand new so I was always assuming that they couldn't possibly be at fault. I now know what it feels like to stop hitting your head against a brick wall. Thanks to Bob Coiro especially.
John and/or Bob,
Why the big change using the Motorcraft F11 plugs? I'm running new Champion A25 plugs. No problems so far, but I'm curious about the improvement with the F11 plugs (?)
Thanks.