Cavalier - Chevrolet :: 1998 - Running Hot / Temperature Begins To Rise Within 60 Seconds

I have a 1998 chevy cavalier, 4 door, 2.2 liter SOHC, which has been running hot for a while now. readings are off the dash guage, here's the scenario. on startup from cold, the temperature begins to rise within 60 seconds, reaching what i consider normal operating temperature within three to five minutes, at approximately the "NO" in " NORMAL" on the gauge.

It reaches what has become it's usual operating temperature, at "RM" within another minute or two. If i am in stop and go traffic, the temperature will rapidly reach the final mark after the "L", but not the red zone. If I get on the highway, the temperature will reduce back to the "RM" position within one to two minutes, three to four minutes in steady traffic at lower speeds, i.e. 35 and all green lights. Thermostat has been replaced, water pump has been replaced, electric cooling fan is running correctly, radiator is free and clear of debris.

When I first got the car back in 2000, it ramped up to heat much more slowly, and hung out at "NO" in all types of traffic. in 2004 i went and picked up my car from my father's place, he had taken it to the local shop and had it given the once over, which is when this problem began showing up, and has gotten progressively worse over the years. I've gotten nowhere with other mechanics, the system is leak free, and the coolant tests good.