just rebuilt runs bad

I think at that point you've exhausted all avenues and the shop should as Old said, if the shop had scruples, they would be offering to come over after work and if nothing else, work WITH you.
You said before they explained why the chain didn't work but you didnt understand. Can you get them to go over it again and you write it down? You don't have to understand at this point... Tell us what they told you, and maybe we can help you understand it.