sheet metal is the direct ground path and the frame is an indirect ground unless you go from engine to frame up front....sheet metal has always seemed pretty iffy to me, but, with a good ground from engine to firewall, it gets a lot better.
Too bad you did not check the voltage drop with your meter on the ground side....I am always interested to see what is going on. That is the next project on my Challenger as the sender resistance seems to have gained a lot from the tank to the dash....wonder ing if it is the ground side that is causing it.
