Thanks for the tips. I moved my htaccess canonical redirect to the top and removed the error documents. For the longest time my zencart page not found/error didn't work, but it has been now for some time: http://www.prommart.com/x

The rest of the stuff...mod_expires and mod_deflate...I got from one of my Prestashop test carts, whose admin can really compress and optimize code. Don't know if it's actually helping, but gtmetrics speed test seems to like it.