Stephen;
Jp has given you a good place to start from. There are three places were grounds are located on this model. Under the left side step plate cover you will find a bolted ground, on the left inside below and behind on the vaporizer - regulator side is another bolted ground connections and on the fuel lock off is the third ground connection. One other item you might look into is corrosion at fuse box. Did you, when you were switching parts, switch the injector driver? This is the small square black box mounted next to the ECM on the left inside. This is only used on Platium I series (LO1/LO2).