gas guage and tachometer have issues

i have a 98 z71, 350 4x4, most of the time my gas guage works fine except for the fact that the needle vibrates, but when i go on long trips after like two hours of driving the gas guage stops vibrating and where it stops vibrating it will not move at all anymore until i shut the truck off and let it sit for awhile and at the same time that happens the tachometer also stops working, it still works but it will get stuck and not move freely so any help with this would be appreciated

i also have a 98 z71 my tach doesnt mess up but my gas gauge is doing the same thing "ghosting" vibrating so fast it looks invisible...it only started after i changed the fuel pump, never did it before my dads 97 z71 does the same thing with the gas gauge. i still havent figured it out either, thougt id just let you know that your not the only one.