Cisco T1 Clocking Promble (The magic non-existent clock...)

I am trying to eastablish a T1 link between two building about 4 miles apart. (No, installing fiber is not an option and there is no line-of-sight.) My company is in a small town that seems to have only recently removed tin can and strings from its phone system.

This should be simple. Except of the DAC at the CO it, is essentially a direct link. We are using two Cisco 2651's with internal CSU/DSU's. We defaulted the config - Extended Super Frame, B8ZS, no FDL. We tried to supply clocking as directed by the telco. However, the two sites would NOT communicate when I configured one router to supply clocking. Only when we removed the clocking would the connection work. The link will stay up for 3 to 4 weeks at a time, but will then go through a period of frame losses that last from 3 to 4 hours. The phone company says it is my problem and that I need to supply clocking. However, the link only works when I do NOT supply clocking.

Any suggestions or ideas how to proceed.

BTW: ALL of my equipment (the routers and CSU/DSU cards) have been swapped out to eliminate bad equipment at my locations.

Thanks, Jim