After this original post, I took the car into the dealer. They diagnosed carbon tracking - leading to new plugs and leads. I guess it was time for a new set, but it still didn't fix the problem.
I will try the battery trick tonight.
I was thinking that the computer had lost some adaptive settings after the battery change and didn't learn correctly after I put the new battery in. From what you say, I should try another reset (I guess you imply that leaving power off does this and and since I don't have a handheld that will have to do)
I also came across another post.....
http://www.carcomplaints.com/Buick/R...999/tsbs.shtml
specifically-
VEHICLE SPEED CONTROL
TSB #050604058 -- INTERMITTENT CHUGGLE OR FISHBITE ON LIGHT ACCELERATION OR A HIGHWAY SPEEDS WITH NO DIAGNOSTIC TROUBLE CODES (DTCS). *TT (NHTSA ID #10017568, SEPTEMBER 01 2005)
Two things additional posts recommed are the TBS and the MAF sensor. I'll try testing the TBS with a voltmeter tomorrow if the battery disconnect doesn't fix it (should be a linear 0.4V to 4V output right???).
Cheers....