Chevrolet Repair: rv temp gauge going high in stop and go traffic, clutch fan, radiator cap

Question
I have a 1994 motorhome with a 454 chevy.I just purchased it at the end of last year.My first long trip was in april and temps were still cool so I didn't have a problem,but last week on a trip I noticed that the temp gauge goes up high.not in the red but just shy of it when im going slow  in traffic.When I get moving again the temp gauge goesback down to half way.I had a new water pump put on when I first brought the rv(it was leaking).They also replaced both exhaust manifolds,which I've read crack from heat.The radiator is full.I took radiator cap off and checked.What could cause the temp to go up so high.And yes the fan is turning.Thank you.

Answer
Hi Jeffery... check to see if the core of the rad is plugged not allowing air flow....if ok you may want to install a cooler thermostat...say a 165 degree...if that doesn't help try going to a fan with more blades on it...also if it is a clutch fan maybe change it to a direct or check to see that the clutch is engauging properly as the engine heats up. i had one with the same type of problem and i solved it by installing an electric fan in front of the rad that i could turn on in traffic...hope this helps