Have a 1968 firebird with a 1970 455 propably doesn’t have 1500 miles on it just had the heads redone again. Because they were messed up. I put the engine back in Had the car running great and took it to a gas station to fill it up with fresh gas 93 octane about 15 minutes away. Then drove home my son wanted to take a ride so I took him out the road and when I turned onto the next road I mashed down on it and it launched then something changed and it started missing so I drove it home it won’t idle now I have checked plugs and wires all firing actually charged plugs I pulled the distributor it looks fine reset it several times and still having the same problem. My father suggested it jumped time but it has a fairly new double roller timing chain anyone have any suggestions?