In my nbs I ran nothing but super in it since 40k and could do 400 to a tank on a road trip and 350 miles in city Can't see a 350 doin that. Idk I thought my 5.3 got decent Milage for a four door
Could be completely wrong but maybe timing is off? Maybe someone replaced the chain and have it off just a tad? Had that hard start problem on a Honda when I did the timing belt and didnt check the marks on the crank but never messed with a chain. Again I could be way off on this one