It seems like it's cooling problem is caused by a lack of circulation, a lack of volume and or a lack of heat transfer to the coolant. You've replaced the fan clutch (hopefully it has a lot of resistance) so presumably the fan is pulling enough air at idle to cool and a new water pump to make sure circulation is good. Crud build-up in the block and radiator not only reduce coolant volume but also interfere with heat transfer from the heat source to the coolant be it liquid or air. The heat transfer is increased greatly if the circulating coolant is touching metal. Crud buildup acts as an insulating layer. Cured the problem in mine with two GOOD flushes and sent the rad. out to be re-cored with additional layers to increase the volume. That made it much better. Temp would still rise under extreme conditions. When I eventually replaced the clutch fan (it seized) with a flex fan the engine never overheated again. Although I've not tried it, I think one could pull the manifolds and remove the expansion (freeze) plugs and clean out the block without removing the engine.
Tips; If you're stuck in traffic not moving, shut the engine off. Mine always started easily so I wasn't concerned with blocking traffic. It won't create more heat if it's not firing. If you're moving slow, keep the RPMs as low as possible. If it is overheating, increase the heater control to hot and turn the blower on high. Better for me to overheat than the engine.