It is a toss up my friend. It could be either. I understand your thoughts on the VP. When my ECM died back in 09, nobody could offer me anything better than check your grounds. Heard that over and over. Me, I was sure it was the ECM but had no knowledge to back that up. So i spent a month or more before replacing it. A VP is a big ticket item also and without some other verification we are hard pressed to tell you to buy one and hope it works. I see to many people show up here after spending 2, 3 or 4 grand chasing problems with parts with no solutions. Dont want you to be one of these folks.