Recently my local auto upholstery guy who I've been using for years said the ACC carpet was about the best going, I was VERY surprised by this.
5 years ago when my car was restored my restorer, after TRYING to get the ACC carpet to fit literally ripped it out and threw it out!
He found a company called TRIM PARTS that had carpet available for my '65 Convertible and he installed IT, mind you it was better than ACCs, but a long way from the fit of NOS FORD carpet.
It seems SO simple for such a large company as ACC to just take a floor pan from a given car and mold it right for the first time, but I guess not.
I really never hear any rumblings from the GM crowd as to who they source their carpets from......sure would like to find SOMEONE that gives a crap enough to make a good fitting carpet!