If you have a T1, pri or otherwise that teminates in a Telco switch you must time off them. If you are having slips it can only be your problem not Telco's. If Telco had a timing problem they'd would be effecting everybody. Reseting your equipment will only work for awhile as it will eventually get out of sync again.
Pure slips will not cause errors, but massive errors can cause slips. So in answer to the Telco telling you he doesn't know if the timing issue cause the errors that answer would be no it wouldn't. So if he was seeing errors and slips it wouldn't be strictly a timing issue and Telco would need to check further.
