fuel tank question

Just bought a 2003 2500 hd with the 6 liter motor. Noticed that when I am driving the fuel gauge keeps climbing. Start off with half a tank and in a couple of miles shows full. When I stopped to fuel up and turned the fuel cap, it made a sucking noise. When I got home looked at the fuel tank and noticed that it looked like it had been "sucked in" on the bottom. What is the problem and how can I fix it?

Just bought a 2003 2500 hd with the 6 liter motor. Noticed that when I am driving the fuel gauge keeps climbing. Start off with half a tank and in a couple of miles shows full. When I stopped to fuel up and turned the fuel cap, it made a sucking noise. When I got home looked at the fuel tank and noticed that it looked like it had been "sucked in" on the bottom. What is the problem and how can I fix it?

make sure you have the correct cap...there is a relief valve in it ..also if this is serious enough of a vacuum the DTC should be indicating what is in need of attention...there are tests done every time you start the vehicle..pcm will generate a code if the fuel tank has the incorrect pressure/vacuum....

don't fill up the tank and park vehicle...this causes the charcoal canister to get plugged,,,which is just one possible cause..

Thank you for your answer. I have never had this problem before. I will try a new cap and let you know if that fixed it.