I have a 97' K1500 w/235K miles. I replaced my transmission about 18 months ago with a GM serta. Plugs, wires, cap & rotor button and fuel filter replaced recently. Engine idles smooth, accelerates like a new truck after I replaced the fuel filter(what a difference ! ). I have a "bucking" when I accelerate lighty at highway speeds between 55-70 mph. I dropped the tranny in 3rd at those speeds and when I accerated gently and I couldn't reproduce the "bucking". Is there something possibly wrong with the tranny in overdrive or is there another problem else where? The tranny shifts smoothy in every gear. There is a fault code for the 2nd gear solenoid so I took it to the dealer under warranty and they replaced the solenoid but the fault code stayed on. They said there is something wrong with the PCM, some kind of short. What say you.