No tach or speedo

I have a 1995 gmc 2500 with a 5.0 L AUTO 4X4
when I start my truck, very frequently the tach and speedo do not work at all, I believe causing the transmission not to shift. But the other guages do work ( gas. Oil. Temp. Volts). On the other hand when I use my remote starter the tach does work until I turn the key on and hit the brake pedal (clearing the remote starter) then the tach drops to nothing. Any help would be appreiciated, i'm stumped