Don't overtighten the belts, that can cause lost steps. There's a lot of things that can cause lost steps while you're dialing in a new machine, the easiest things to check are the potentiometers (pots), pulleys, V-wheels, and belt tension.
There's 2 threads you may be interested in. I set one up with a bunch of videos I made to help dial in a new machine:
The second thread is a great guide to potential problems causing lost steps:
Check them both out, between my videos and @LarryM's guide you should be able to get everything sorted out. If you can't figure it out, or if you have questions, don't hesitate to ask. There's a lot of great folks on here that are willing to help you troubleshoot problems.