fuel gauge

Hi, I have a 97 Ram 1500. I looked on other forums and on here to try to find my answer and I can't find a problem exactly like mine. So my fuel gauge kind of works. I fill up my tank and it shows that it's full. When I start to accelerate the needle moves down fairly quick to like 1/2 a tank as...

Can anyone tell me an easy way to access the output of the fuel sending unit? My gauge went from reading a quater tank to going all empty after I gave her a full tank of fuel . This is an 01 ram 1500 with a 5.2. This truck also has a faulty PCM that I'm saving up for. Could it be related? She...