In my install of DP (I'm using 1.3 beta 3 in Zen 1.3.7) the file which gathers up the info and displays it is ...
admin/includes/modules/product/collect_info.php
...around line 337.
I've never used Group Pricing, nor am I using either of the other mods you've installed. I have several other mods installed but still DP works fine for me.
HTH
Rob
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