Jordan,
I haven't tried the code with 3.4.x yet. I took a quick look, and you can try this as a debugging step. Backup up your mod_CUSTOM.php file, and replace it with just this one line:
Code:
$intershipper_rates[] = array("methodid" => 201, "rate" => 10);
Replace "201" with whatever subcode you used.
This should give you a shipping option while in your cart for the shipping method you added at $10. Let me know what happens.
Some other quick notes:
Make sure that your insert SQL statement went into the table correctly.
Make sure your products have weights (just in case).
Make sure you are shipping domestically, since the SQL set the method for national only - if not, change it.
Gary