Re: 305 V-6 engine oil
 

I have used Valvoline VR1 high Zinc 30W and 20W50 conventional and 80W90 in transmission and rear end Louie Louie has 305E, 420SM ,307 diff. OE cannister oil filter part # CH106PL all from AutoZone. Good days with your GMC. JF

Re: 305 V-6 engine oil
 

I use Valvoline VR1, it's easier to find while traveling on the road.

Re: 305 V-6 engine oil
 

I believe Valvoline VR1 is what we will be using.Still in disassembly stage.We haven't pulled the engine yet.I'm going to miss firing her up and hearing her run. We just recieved all gasket sets needed so motor will be gone through soon hopefully.Still have to order me a canister oil filter.Thank you all for info.