my rpm's race up to 6000 when I start my engine and then it will usually die

99 GMC Sierra 5.3 235000 miles. When I start it up the RPMs jump up to 5000 to 6000 and back down to under a 1000 and will usually die. If it does not die it is a real low rough idle. When I try to drive the vehicle it will gradually accelerate until I reach about 45 mphs. without pressing accelerator and start surging. when I come to a stop it surges. I have replaced Intake manifold gasket, Mass air flow sensor, fuel regulator, throttle position sensor and pcv valve.