Did you do loopback test from the channel bank? Do you get 500 linecode violations and then no more?
Make sure both the channel bank and T1 interface of the router are using the same linecode (B8ZS or AMI).
Check clocking. Which device is providing clocking for the T1? One device should be doing internal clocking and the other should be doing line clocking.
How long is the T1 cable? Try cablelength short or cablelength long to compensate.
Have you tried making a test call over your 2610? How does it sound to you? There are other things that can account for low call durations like echo, False Answer Supervision issues with the channel bank, volume (gain) issues, not enough IP bandwidth, etc.
Regards