Inewso, are these 6 T-1'r running out of the same cabinet? Maybe there is a problem with the backboard of the T-1 card housing box. We have weird problems before that were affected by temperature changing hot/cold and connections opening and closing. One site had a 25pr amp coming out of the telco feed box that could make and break connections by putting your hand on the amp connector. Try to get the telco to replace the card cage housing or moving one that has problems to a single card housing for testing purposes.....Also try to eliminate as many terminations points from telco as possible, even if it is temp for testing. Hope this helps.