xj throwin codes, need an opinion....

ok the xj threw a code at me on saturday morning(98 4.0 at with a high flow cat and flowmaster exh). immmediately read it to see what my new problem was it came out a p0455 evap emission control leak (large). so i kept driving it, and saw that it was consuming gas at a much faster rate than normal. my instinct leads me to believe that it has fried an o2 but the o2 in the cat is like 2 weeks old. has anyone pulled this code before and do you have a suggestion of what to throw money at first to make it happy again. thanks

-doug-

haha fixed it loose gas cap duhhh i feel stupid:confused1