Hey guys, got a 2007 Envoy with 203k miles. Just replaced the spark plugs about 3 months ago with AC Delhi recommended plugs. No issues since but the other day as I got to about 50 mph my check engine light came on and was flashing. Got home and pulled codes, got a P0303 for cylinder 3 misfire so I replaced the ignition coil for 3 since I am assuming the plug is fine being new. Ignition coils were original so common sense. Cleared the codes and drove around town keeping it under 40mph and nothing. Runs smooth. Then I took it on the highway and as soon as it gets to 50mph plus, the check engine light flashes again. This time the codes were for cylinder 3 and also P0300 for random/multiple cylinder misfire. As soon as I lower my speed to anything less than 50mph, the light goes away completely. Other than a loss of power when the light comes on and flashes at higher speeds, it doesn’t seem to run rough at all. If I sit at idle in park and rev it to 5k-6k rpm nothing happens, it only throws the codes when I’m going at faster speeds. Any ideas?