IMO do not experiment with torque ratings. Go with what the manual suggests.
It is really not advisable for any mechanic to deviate from the ratings as specified by GM engineers, unless GM changed the specs via a Technical Service Bulletin. Such 'TSB's are sometimes available on-line.
However, IMO torque to what the manual says and do not worry about what some mechanics allegedly do. IMO the GM engineers know more and stated torque specs for very good reasons.