Code PO351 again, now what..........

Hope somebody can help me out, my '01 4.3 Blazer Extreme started missing and threw a P0351 code (Ign. Coil Primary/Secondary Malfunction)when the check engine light came on. I replaced the ignition coil, and since it had 70K miles the sparkplugs and fuel filter also. Great, the missing,stuttering and occasional backfire was gone! Two weeks later, same problem came up again, again code PO351. Noticed when I replaced the coil the first time, the box had been opened and the mounting screws were not in the box, indicating it might have been returned (as defective?) so the parts store exhanged it for another new coil. Put new coil on and problem solved! or so I thought, 10 days later, same problem is back!! First coil was not defective apperantly. Let the car sit a bit either at idle or engine off and it was able to get me home again, if I was real easy on the throttle. Starts just fine hot or cold, what do I check next so I repair this problem? It's so odd that replacing the coil will fix it for a week or so and then the problem comes back. Thanks in advance.....

Hope somebody can help me out, my '01 4.3 Blazer Extreme started missing and threw a P0351 code (Ign. Coil Primary/Secondary Malfunction)when the check engine light came on. I replaced the ignition coil, and since it had 70K miles the sparkplugs and fuel filter also. Great, the missing,stuttering and occasional backfire was gone! Two weeks later, same problem came up again, again code PO351. Noticed when I replaced the coil the first time, the box had been opened and the mounting screws were not in the box, indicating it might have been returned (as defective?) so the parts store exhanged it for another new coil. Put new coil on and problem solved! or so I thought, 10 days later, same problem is back!! First coil was not defective apperantly. Let the car sit a bit either at idle or engine off and it was able to get me home again, if I was real easy on the throttle. Starts just fine hot or cold, what do I check next so I repair this problem? It's so odd that replacing the coil will fix it for a week or so and then the problem comes back. Thanks in advance.....
I would start looking for a broken wire, bad connector, going to the coil pack or to electronic control module. Also check the grounds on the back of each head. GM is known to have faulty connectore and grounds.
It sux that your extreme is that new and already having those kind of problem. I hope this helps. If worse comes to worse, you may want to replace the control module. I've had 3 GM's the kept eating coils right and left. It seemed like every time I turned around, one of the coils would go out. I took it to a deal and paid them 138 dollars to fix it. They said I had a fraid wire on the connector harness and they fixed it. Two days later, the same problem occurred. I finally replace the electronic control module and didn't have the problem any more. I still have that vehicle and runs great to this day. It's been 3 years since replaced the module. I'm not saying replace your module, but it sounds like the problem I had. Good luck.
Southern.