Help STILL OVERHEATING

Hello -
I just had my oil pump, timing belt, crank and cam seals (I think) and thermostat done. I am wondering why the car still over heats ?!?!?
When driven softly - gently - it is not much of a problem . Most of the time. However on occasion I can see the guage creep up and then go down as it gets closer to the H - generally I have the A/C running (even though I have no blower motor) - to keep the engine cool.

When I drive it hard - I get the same thing - except that the guage may even go to the red area and it does not come down as fast.

Any insight will be appreciated. Do you think the mechanic did not change the thermostat?

Also the coolant resevoir look like it is 'steaming'? Commuter SVX will verify this last part as he came by and looked at the car.

There is no smoke coming out of the exhaust - so I am not sure if it is a head gasket leak.
ALL HELP IS APPRECIATED.
Thanx