@@Tsimi, thanks for the reply... I hadn't logged in in a few days. I went back and found I missed one line in one off the class files. Fixed that and it worked. Should have updated this thread but I had posted in a ton with the number of errors I experienced and couldn't remember them all.
Here's how I modified mine for the invoice number. Right before the line
$params = array('x_login' => substr(MODULE_PAYMENT_AUTHORIZENET_CC_AIM_LOGIN_ID, 0, 20),
// A.NET INVOICE NUMBER FIX
// find the next order_id to pass as x_Invoice_Num
$inv_id = tep_db_query("select orders_id from " . TABLE_ORDERS . " order by orders_id DESC limit 1");
$last_inv = tep_db_fetch_array($inv_id);
$next_inv = $last_inv['orders_id']+1;
// END A.NET INVOICE NUMBER FIX
then you'll need to add this somewhere in the array
'x_Invoice_Num' => $next_inv,
And that will transmit the invoice number.