Stuart, my gauge is electric and the old sender on the 228 was gas filled. It was gone when I got the engine. Since the electric gauge is 12v and works, it appears to be simply a problem of getting a sensor that more closely matches the GMC gauge temp range and not the Chevy gauge temp range. If you add resistors of any value to the sensor wire, they either peg the needle or make no difference. Think that's because of the NTC sensor as one is increasing resistance rather than reducing resistance. I guess one solution would be to get a 12v Chevy gauge, cover it with a brown decal to match the GMC gauge colors and see if that works. Anyway, not a big deal as the truck runs fine and doesn't overheat.
