Your truck has only one module(with exclusion of the PCM) which is the TIPM and is located on driver side under the hood. Little black box in front of the battery. But I agree with Tommycat, it sounds like a loos ground or connection somewhere. there is also a sensor in your Differential housing( at the top of the "pumpkin") which should be the only speed sensor on the rear of your truck. but check the connection on that as well. It is also a magnet, so metal could stick to it from the inside.
2WD-Dsp 93 tune-55 series tires-3.92s-PacesetterLT Headers w/ 3in catted y-pipe- DynoMax Race Bullet- 2.2K ohm power wire- hellwig rear sway bar- 190 Degree Thermostat-