G'day Dave,
I was going to set up this weekend to do some testing etc, but just remembered as I type this that I have a 40th to go to. I'd rather be imaging
I can't come around in the next week or 2, but keep me posted if you continue to have problems or if you've solved them. Can't help with the powertank issue, but can help to look at the focuser, balance and your polar alignment etc.