Did you solve the overheating problem?
If you had a single cylinder misfire, due to any reason, it should show up in your cylinder balance test.
Is it a single cylinder misfire?? Cylinder head cracks let water into the chamber and cause misfires at idle. If they were large enough to misfire beyond idle they would eventually fill a cylinder (while shut off) and prevent starting due to hydrostatic lock.
Timing issues can cause overheating; did the overheating go away? If so thats not an issue.
Hard to make recommendation against the data supplied. If you have a single cylinder misfire it should act like a single cyclinder misfire.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician