This may seem a little basic for most of you. I have a 55 GMC with a 288 V8 engine. I live in an area with mild winters and hot summers (but I don't plan on running it to much in either of those conditions). What engine oil do you recommend I use? (weight & grade, I don't want to get people going about their favorite brands) Right now it still has the GulfPride that was put in it 30 years ago.(20wt I think, I will have to look).