You want to get yoru car fixed, right?
Plus you're upset with their customer service, right?

Bite your lip, let them finish fixing the car. Then when its done and they've invested their money and they call you to come pick up your car thats when you open your mouth.

You can remind them of their terrible customer service. You can tell them that you are not willing to pay $800 for replacement of the PCM just for troubleshooting purposes. If they can't proove the original was bad then you will not pay any costs associated with its replacement because there was nothing wrong with it. If they give you any static just remind then that you still have your money, their bill is outrageous, they treated you as if you were wasting their time when in fact you are a coutomer and they took the fact that you are not technically inclined to their advantage so they could extort money from you.

If you are willing to cut your loses in a worst case scenario make them a take it or leave it offer of what you are willing to pay.

This is really burning me to hear these stories about what is going on with your car. I wish there were more reasources available when you were doing the work yourself so you could have fixed it yourself rather than have to deal with a bunch of jokers.

I feel sorry for the people who don't drink. When they wake up in the morning, thats the best they're going to feel all day - former President Lyndon B. Johnson