Frustrating work

I'm struggling at work. It's very frustrating. I designed a backplane, Rev 0. Everything worked ok with the prototypes, except the regulator circuit was a teensy bit small for the current we were drawing. So I beefed up the regulator circuit without changing anything else. It was a small enough change that my boss decided to buy 50 boards.
So Rev 1 comes in, and a big section of it doesn't work. So I've spent the week trying to figure out why, and I'm getting nowhere.
When we placed the order, the boardhouse, that makes the bare printed circuit boards, had a hard time meeting my impedance requirements. They had to scrap their first two lots. That's very unusual and costly to them.
I can easily see some manager saying, "We are not eating the cost on this again."
My theory is that they fabricated the board with either borderline impedance or flat out bad. When you're dealing with GHz frequencies over several inches, this is significant. I am already pushing what is allowed by the spec. The last thing I need is a faulty board.
But I've been troubleshooting like it's not the board material, but I'm getting nowhere.
The pressure is on. If I can't prove that the problem is in the boards, the owner will suspect that it's something I did. 50 boards are expensive, and we've already lost a customer because we couldn't deliver on time.