What grade gas should be used ?

You should always use premium fuel on the high conmpression V8 engine. Cheaper fuel can cause a PING, and possible engine damage. 87 octane is definitely not recommended at any time, but sometimes you can get by with 89 for a small period of time.

Gas mileage and power will both be down with lower octane fuel, so do not use it all the time.

Usr 87 octane found at most pumps as regular, higher octane will not benefit you in any way unless you live in a high altitude area