it seems yer not starting or seeing the first digits, with a W body car, the 10th digit is always a W, g/h body will be g or h in the 10th spot, look two to the left, it will either be a K or a 1 for a 3800 powered car. i cant remember the vin for the 3100/3400v6.

both of those gtp's should have a 1 in the 8th spot