I just purchased an 05 and the previous owner swapped an LQ9 block and kept the 243 head from the LS2. About 15 minutes after purchasing the vehicle I got on the highway and the check engine light started flashing. I pulled over to scan the code and it was for a random misfire, but the vehicle doesn’t seem to be misfiring at all. The previous owner said it needs to be taken to GM for a “case variation relearn” to set the timing correct. Has anyone had a similar issue? Or should I expect something more serious?