PSInt said:

20,000 per change ?? Is that the accepted interval with synthetic ?? I've been toying with the idea of synthetic oil but couldn't find the recommended interval. I've heard the fuel mileage picks up a little with synthetic also. Is that true ?? So much hype out there you never know what to believe.

My 96 gets 14 MPG on it's best day and usually closer to 13. I'm not really happy with that since others are approaching 20 MPG. I bought the tools to set the timing but haven't gotten around to it yet. I was amazed that the #5 plate I installed didn't hurt my fuel mileage, however it sure woke up the power.

Curious as to how much mileage gain is realistic by switching to synthetic.
From the Amsoil website regarding drain intervals.
Normal Service
(3) -- Up to 25,000 miles or one year, whichever comes first, or longer based on oil analysis.
(3) Personal transportation vehicles frequently traveling greater than 10 miles (16 km) at a time and not operating under severe service.
Severe Service
(4) -- Up to 15,000 miles or one year, whichever comes first, or longer based on oil analysis.
EGR equipped or low emission diesels -- extend drain intervals based on oil analysis or use the longest drain recommendation of the OEM*.
Replace Donaldson Endurance™ or AMSOIL Ea™ full flow oil filters at the time of oil change up to two times (2X) longer than the OEM* standard interval, not to exceed 60,000 miles in long-haul trucks.
OEM = Original Equipment Manufacturer
(1) Engines operating under modified conditions are excluded from extended drain recommendations. Examples include the use of performance computer chips; non-OEM approved exhaust, fuel or air induction systems; and the use of fuels other than those recommended for normal operation by the manufacturer.
(2) Engines are in good working condition and within the factory design settings. Mechanically sound engines, for example, do not leak oil or consume excessive amounts, are not worn out, do not overheat, do not have internal or external anti-freeze leaks and have a properly working emission control system. AMSOIL recommends repairs be made to malfunctioning engines prior to the installation of AMSOIL synthetic oils.
(3) Personal transportation vehicles frequently traveling greater than 10 miles (16 km) at a time and not operating under severe service.
(4) Extensive engine idling, daily short trip driving less than 10 miles (16 km), frequent towing, plowing, hauling heavy loads or dusty-condition driving.