I have an 87' Trans Am 350 TPI and no matter how full the gas tank is the digital dash always says I have a full tank. I'm assuming the sending unit is bad and if theres an easy way to change that? but any other input on the gauge is appreciated. Thanks!

 

there are posts detailing how to cut a trap door...did it on my 87 TA and its great

 

Cutting a trap door is one solution to getting to the fuel-pump/float level unit.
The other is drop the tank. Like a religion, each has its apostles & disciples.
Caveat Emptor.

I would suggest an easier alternative is to first verify the lack of signal into
the instrument panel. There is a three wire harness to the fuel tank,
that can be disconnected from the body panel. The three wires are ground
(black), switched power in (gray), and fuel level out (purple). The fuel level
varies resistance from 0-90 ohms. Measure resistance between purple &
black, when you estimate approx. half full. If you get a reading anywhere
near 45 ohms, the level sender is functioning, and the problem is with
the gauge unit itself -- unusual, but not impossible. (Go ahead, ask me
how I know this. )

Good luck, & keep us posted.