OK, a few things. Check your coils for excessive resistance on one side. The ground is a good idea. I personally like to run one directly off the negitive post to a bolt for the body. Sounds strange, work well. Could be a CMP or CKP starting to loose sensitivty. Also, try taking it out, finding a good long stretch of road, and maxing it out. If you can get above 70 in less then 10 minutes, try and trade it into a GM dealer as a "high performance model" Seriously though, try running a bottle of fuel injector cleaner through it. If the system senses a lean fire, it will try to double fire the injector, causing a surge in RPMs. Sounds stupid, but try it. A injector the size of a pin clogs very easily