high temps. in traffic

My '95 C280 runs very hot while in traffic. The fans still come on but only briefly and not enough to bring temperatures back down to normal. Once out of traffic, the temperatures drop back to normal. Temps are about 79*C while driving and over 110*C while sitting in traffic. I've already replaced the temp. switch on top of the t-stat housing but the problem is still there. If I jump the fan switch, the temperature stays cool but the fan constantly runs. Anyone have any ideas or solutions?