Had the same problem too. I noticed that right after I bought this truck used, when topping off the fuel tank there was gas underneath the truck. After a few days of driving I had a check engine light with a code P0455 (Major leak in the evaporative system).
Could not feel/see anything obvious on top as all hoses/connections were OK. At the top of the tank were the fuel inlet/overflow tubes and the fuel pump which, by touch, felt OK (I could not see them).
To make a long story short, I took it to my mechanic who dropped the fuel tank and found the fuel pump was recently replaced. The problem was whoever replaced the fuel pump crossed threaded the 6 inch diameter plastic nut that holds the fuel pump to the fuel tank.
This created my "Massive" leak in my evaporative system code P0455!
The plastic nut was only $10.00 but the labor of dropping the fuel tank was $80.00.
Just an FYI for do-it-yourselfers. You should never have to "force" anything to fit. If it doesn't fit right, back off and try again or make sure you have the right part. Then you won't cross thread it.
Once I get the bugs worked out of mine, can't wait to "Get a little mud on the tires"!
2001 Ram 1500 5.9L/360 4X4 SLT White Nothing fancy yet, just a nice work truck! Recent mods are a new TC, TransGo shift kit, Nerf bars and a very functional tool box that has room enough for my golf clubs Just added remote keyless entry and remote starter (worth it's weight in gold on cold mornings!)