Did you consider that at 5200 feet the engine is receiving approximately 25 inches of manifold pressurem versus approximately 30 inches at Sea Level ? - That's a LARGE reduction in power, and accounts for the lower pitch attitude necessary at the higher altitude.
Also, are you leaning the mixture for takeoff? If you are at full rich, you are likely getting even less power because of the over-rich mixture. You will also foul the plugs sooner.