I have had the same 1-2 shudder issue since buying the GP 5 years ago. Did the shift kit in year 2 and change the fluid at least once a year, if not twice. I did throw in half a bottle of Lucas last year, but never noticed a difference. I think I'm one of the lucky one's, as my tranny has acted and stayed the same over the years.

Oh, and my last tranny service (last month) I put in Dex 6. So far no issues.