My high mileage Envoy (163k) has been serviced with 5W30 dino oil most of its life. Switched to Mobil 1 last change thinking it might prolong its useful service. Advanced Auto parts has rotating brand, killer deals on oil and filters. Just bought 5 qt Valvoline full synthetic with a Bosch Distance Plus for $31 before the $7 mail in rebate for my wife's van. Wondering if a designated "high mileage" dino oil offers more benefits than a synthetic at this late date. Probably not willing to spring for higher priced synthetics like Amsoil and Royal Purple. Any thoughts welcome.