1996 Accord weird overheating problem???

[terrypdoherty]

My 1996 Accord appears to overheat when the weather is warm, the A/C is turned on and travelling at highway speed. The needle does not go into the red, but does go quite close. This has started happening recently.
Up until now I have never seen the needle go beyond the midpoint.
Whats odd is that if I slow down then the temperature returns to normal.
Also, the A/C appears to not function (meaning no cold air) when the needle is very high, but when it comes back down below the midpoint then it starts to throw cold air again.
Does anyone know what the problem could be?

[mpumas]

Insufficient water flow through radiator, partially open thermostat (stuck). plugged radiator (flush), radiator/condenser fins plugged with bugs, fans not working (check fuses) are possible causes.