I have a Trek 4900 that was recently serviced for slipping. They replaced the rear hub and the chain. I am somewhat a novice at bicycle repair. The bike still slips and they cannot reproduce the problem. I have been trying to troubleshoot this and the only thing I can figure is the chain they put on a HG-58 chain when the chainring says "Use IG Chain Only". It is also possible the chain rings are worn out in which case: should I use this opportunity to change it out to a non-IG model? It is a Deore Mega-9 derailer in the back and a alivio in the front. Thanks in advance.