Check this out...
Bennie, from Hesco just called... He tells me that the 99-04 Wrangler all come with his type of impeller already on it. Granted, not the metal one, but plastic, but still his design. He then proceeded to tell me to check for a cracked head or maybe a lean condition. (which I honestly have not checked for, as this problem has been happening since it was pretty much new). He continued to say that the 0331 heads had a high probability of cracking. Though Jeep never issued a bulletin, they were just waiting for them to be returned for this problem and then warranted out then.
This is the type of customer service I like and appreicate. I placed a $200 order with them and he could have easily sent out what I ordered. Instead he made the effort to call and let me know the water pump was probably not the cause.
A+ for Hesco!!