It's very likely you won't actually need timing chains. The chains are usually in good shape and very serviceable unless your tensioners have failed in such a way that the chain gets damaged. Replacing just the tensioners should do the job without having to replace the chains. Having said that, the OEM chains are not all that expensive really if you want to change them out. I just saw my timing original timing chains (I've been the only owner and bought it new in 2006) today and they look like they are new still. I have just over 120,000K on the truck. 2 out of the 3 tensioners were worn badly. Actually, the tensioners themselves weren't worn, but the plastic/composite guide rails were. Still with the 2 in bad shape, my truck wasn't making any terrible noises. Had I not had a low oil pressure at idle issue, I would never have considered replacing the tensioners and guides.