Can anyone diagnose this overheating problem

[Barnsnake]

I'd start by verifying the accuracy of the gauge/sender. Your description of a consistent (although high) temperature reading before the service makes me doubly suspicious of the gauge. If there are alternate locations for the sender, use the location nearest the engine side of the thermostat.
You seem to be aware of air pocket issues which may arise after any cooling system service.
If the expansion recovery tank's hot and cold levels are consistent, it should rule out a head gasket leak.
If you are using old rubber radiator hoses a "flap" from a failure of the inner lining could be restricting flow.

Keep us posted on your findings.