Right now I have a stash of RGT 5w30 but no vehicle that recommends that. I know 5w30 can be used where 10w30 was recommended. My 88f150 is due for a change and wondering if yall think it will do fine. She's probably got loads of miles and uses oil. She's a flat tappet aswell. Right now I got 15w40 trying to slow its consumption but I have notice it took a hit on fuel milage. Engine is a 5.0L by the way.