Ok, well here's the finale - what was wrong...
After looking at all the symptoms, being;
- pressurized rad hoses when cold,
- air / liquid surge into overflow tank when loosening cold rad cap,
- constant bubbling off in overflow rad tank when running,
- pressure being maintained when cold and not leaking off,
- no rad fluid on ground, no other apparent leaks,
- no white smoke in exhaust,
- oil not white / opaque,
- rad fluid not brown / oily,
- no pooled fluid near intake manifold gaskets,
- steady (non erratic) idle
- loss of heat in cabin when idling long time
- waterfall swishing sound when cold startup
I used my home gas detector (propane / natural gas / co2) to check the air coming from the rad when I unscrewed the rad cap and it all gushed into the overflow tank. Upon doing this, I got a GAS alarm... so it was propane in the rad and not air... no wonder I could never bleed it out.... propane converter was leaking propane into coolant system. After turning off propane system at tank and re-bleeding system, no more problems. No more gushing sounds under dashboard. Changed propane converter and am running on propane again for last two days - all is gone.
Thought you might like to know.
Thanks for the help!