My truck, in sig, has had a constant diet of syn oils since new. It's had M1, Syntec, SynPower, & PP during the first 108,000 miles. I have always done OC's based on the OLM. I was going about 7500 miles for a OCI depending on how much I towed. . In the last year or so, my driving habits have changed with alot more short trips, not much towing. My last couple of OC's have been in the 3-4000 mile range, and I just changed the oil Saturday and OCI was 3075 miles. I used some Quaker State Conventional with a Puro classic. I'm thinking that I'm just wasting money using syn at this time. I guess my question is, since this truck has seen nothing but syn for it's entire life, minus the FF, is going to a dino going to cause me any problems. The truck runs great, no mechanical issues, well I do have a power steering leak I need to address.