I would go get a new thermostat to start. Then if that doesn't fix it, take a look at the water pump.
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2007 2500, QCSB, 4x4, 5.9L, 48RE, silencer ring MIA, torque tube baffle MIA, B&W Hitch, Smarty Jr POD, Isspro gauges (boost, trans temp, EGT), Aero Turbine 4040XL, smoked cablights