Edit-page half-loading with PHP 5.3 CGI

My webhost, as default, uses PHP 5.2.x + FCGI. I was getting a lot of 500 errors (premature script header) which I traced back to one of my more useful (though memory-intensive) plugins not really cooperating with FastCGI. Anyways, I switched to regular CGI to see if it helped. When that worked, a few days later I also upgraded the PHP to 5.3.x.

Anyways, once in awhile now, when I go to edit certain longer pages the editor will only half-load (e.g. the top half of the page. The editor box shows up but no text inside).. A refresh fixes it but it can be pesky. Nothing shows up in the error log.

Does anyone have any suggestions? Switching back to FCGI isn’t an option due to all the problems. I’d rather not disable all the plugins and I dont even have the default theme. I can live with it but if anyone has any suggestions that be appreciated.