from '08 Expy Owners Guide page 6:

"BREAKING-IN YOUR VEHICLE
Your vehicle does not need an extensive break-in. Try not to drive
continuously at the same speed for the first 1,000 miles (1,600 km) of
new vehicle operation. Vary your speed frequently in order to give the
moving parts a chance to break in.
Drive your new vehicle at least 500 miles (800 km) before towing a
trailer. For more detailed information about towing a trailer, refer to
Trailer towing in the Tires, Wheels and Loading chapter.
Do not add friction modifier compounds or special break-in oils since
these additives may prevent piston ring seating. See Engine oil in the
Maintenance and Specifications chapter for more information on oil
usage."

It is really amazing how many people do not read the owner's manual. Who knows why, but it's a fact. The owners manual has almost everything that you need to know about your vehicle. Its a big book, owners paid for it, but it wastes away in the glove box or in the trash. Too bad.