Sorry for the long delay. I actually didn't notice the question the first time through..
We only use best sellers on the home page but I did find the code your looking for to fix this on the products page.
locate this in product.php:
Code:
if ($active_modules["Bestsellers"])
include $xcart_dir."/modules/Bestsellers/bestsellers.php";
replace with
Code:
require $xcart_dir."/modules/Bestsellers/newbestsellers.php";
Also if this is being displayed on the shopping cart then you will need to edit cart.php and add...
Code:
require $xcart_dir."/modules/Bestsellers/newbestsellers.php";
...somewhere to the end of the file before func_display (I believe).