92 firebird gauge problem

The friggin speedometer and tachometer arent working properly in my 92 bird with the 3.1L. When im cruisin on the highway at 70mph the speedometer will read about 28-30 mph. Crankin the engine up to about 3000 rpm's registers about 1500 rpm's. I figured the speedometer problem wouldve been the speed sensor on the trans. tail housing, but the tachometer has me thinking its the instrument cluster. All other gauges work properly from what i noticed. Just wondering if anyone else had this issue. Appreciate any help.

i think it's probably the speed sensor if you have analog guages.