If you had a bad spark plug, replacing it with any brand plug would have solved the problem temporarily. If there is something causing the plug to foul out, such as a leaking valve stem seal, it will foul out the Pulstar also over time.

Did you do it yourself or did a mechanic change the plugs? Where the plugs that came out original or did someone before you put in the wrong heat range? What was the condition of the plugs when they were removed? It's possible that one of the wires was not attached correctly and now after replacing the plugs, it's back where it should be.

I had customers that swore that when they replaced their spark plugs with another brand it ran better. It's mostly perceived. If it did run better it's because a plug or two was fouled and any brand would have made it run better.

Let us know how you make out. Good Luck