I have new 383 engine in my 94 k1500 and started right out with Mobil 1 5w-30 and will continue that forever. I know it probably doesn't need to be changed for several thousand miles. But this vehicle is used for towing a travel trailer so based on my long time experience with oil changes (always used Havoline 30 back in the '60's, 50 cents a can) I can't stop myself from changing it every 3,000 miles. Makes me feel "clean." Use AC or Wix filters. back in the '60's I was working at an auto parts store that became one of the first Carquest stores where i was introduced to Wix filters.
Also have a 1965 Chevy Van with a 292 that I installed in 1988 to tow a travel trailer. Towed with it for 90,000 miles, extremely torquey engine, still runs and still tows but is in storage. After we bought an '88 Burb 454, van went into 18 years of storage. Started right up after that but started running real bad. Turns out that I didn't know that most of the zinc and phosphates had been removed from oil so Mobil 1 5w-30 didn't work so well, lifters started making noise. So switched to Valvoline Racing Oil 20-50 which has lots of zinc, after replacing the lifters. Runs good now. Also didn't realize that the carb would not like the ethanol which ruined the gaskets. So rebuilt the Weber 36-36 with new gaskets and started using Seafoam and Stabil in the gas tank. Use it before putting it back in storage, add some new gas, run the carb out of gas before shutting off the engine. I have an electric fuel pump that is wired direct so I can shut it off while the engine is running and eventually runs out of gas and stops.