Factory Tach and gas gauge

[danadena1960]

I have a 1977 K-20 with a factory tach in it. The tack seems to be about 2k off, high. When I flip the dual tank switch the tach jumps but still reads high, has anybody seen or have any ideas on this problem? Also, seem times the gas gauge works and some times it doesn't. It seems like when the truck sets for a few hours it works and after she gets warmed up, it goes to "E".