Cisco WAN :: Moving T-1 From 2600 To 2911 Router?

We have an old Cisco 2600 series router, running a single T-1 line, AT&T is the carrier. Very standard stuff.
 
The T-1 works perfectly on the old router. Cisco 2600 with a WIC-1DSU-T1 card. We have a brand new 2911 router with a VWIC3-1MFT-T1/E1 card in it. The circuit runs 100% clean and trouble free on the old router. When I plug it into the new router, it shows up/up but has a massive number of errors on the line, and the circuit is not usable. There are no timing slips or anything like that.
 
I have another site using the same router and card with the same configuration on that T-1 and it works perfectly. Zero errors. This site (in a different city) is totally slammed with errors. We already replaced the T-1 card and still have the exact same issue.
 
I've actually been doing this a long time, and I've tried all of the usual things, adjusting line build out, changing clock source, checking and re-checking configs. Nothing seems to reduce the error rate.
 
I personally think it has something to do with the Smartjack. Like maybe their LBO is too high or too low, and the old router card was more/less sensitive than the new one?
 
This is a layer 1 issue and is not defective hardware or defective configuration. I am looking for T-1 insights or bugs/issues.