If you have the ralley dash, your fuel gauge could be the cause of your gauges reading too high, as the voltage limiter is part of the fuel gauge, and could cause the gauges to read too high or to low if it malfunctions. Happened to my 340 duster, all three gauges, (temp, oil press and fuel level started reading half of what they should have because of the fuel gauge. I imagine a non ralley cluster may do the same if plug-in style voltage limiter freaks out. Head gasket re-torqing is seldom done, so if the bolts were torqued to correct specs, it should not cause a problem.