Hi marcshunk,
First of all since the pairs are leased as ckts from a telco or service provider, you need to get them to redesign the loops with voice repeaters on each one with no more than -3.0dB loss end-to-end. I would start by opening trouble tickets with repair service and escalate from there. Over the years this has always been a problem with off-prem stations on copper. The losses are additive so you want to make sure your trunks have good levels also. Whenever I ordered OPS ckts from the telco, I always specified a -3.0dB loss design - NO EXCEPTIONS - Since you mentioned levels I assume you have test equipment to do measurements. But with only one TIMMS that could limit you somewhat.
You have another option here and that is to move all the off-prem stations to a point-to-point T1 ckt. I believe Northern Telecom makes a T1 station card for the M1 switches. I know they make one for trunks! (Why they did not just use one card for both I have never figured out.) On the station end you would use a channel bank with FXS cards and on the switch end use the T1 card. There are some nice channel bank packages available. One that comes to mind is the Carrier Access ADIT600 which has lots of flexibility and can support 2-T1s for a total of 48 channels and is very small.
Now obviously there are costs involved with this. Not knowing what your situation is, changing to a T1 could save you or your customer money and provide more options if you needed to haul data to/from the same location. Plus you are in control of the levels at this point and can taylor the design as needed.
Hope this helps!
JIM