[chev3600]

I wish I had a similar setup! I have seen cooling issues on many different vehicles. Some resulting from inefficient electric fans, no shrouding, fan too small, etc. Also ignition timing / lean mixture can cause it to run hotter. Your rad sounds like its fine. Is the fan the largest size you can fit? I've even run a hose on a radiator while idling to see if reducing the temp will be enough. Just a small spray to cool it down a little.

Just some ideas, hope it helps.
High pressure cap? no 3-6 lbs.