Ford Repair: Engine cutting out on F150, half tank, tank problem

Question
I have a problem with my 2004 F150 with 5.4L engine.  When I have less than half a tank of gas left, the engine tends to cut out when I try to accelerate quickly or go up hills (i.e. an uphill onramp).  The more throttle I give it, the worse it gets.  However, when the tank is over half full, this problem goes away.  It's almost like it's running out of gas, but there is atleast over a third tank left.  When this problem occurs, I can cruise down the highway ok with no loss of power, but if I accelerate to pass, it starts cutting out.  Now today, my emission light came on (with a full tank) and has stayed on.  I checked my fuel cap to be sure it was on tight and correctly.  Still no fix.  The obvious things don't seem to fit the full tank/half tank problem (i.e. fuel filter, bad gas, etc).  Are these 2 related or seperate issues?  Any help would be greatly appreciated.  

Answer
These two could very well be related. The fuel system is closely monitored for leaks or pressure changes. This sounds to me like a crack or leak in the flexible tube that connects the pump in the tank with the output connector. Can't say that I have seen such a thing, but it is possible.

First thing you need to do is find out what code turned the CEL on, and either let me know or have the shop or dealer check it out. Chances are there will be a code to lead the tech in the right direction. If your truck is still under warranty, that would be great. If you have a place like Autozone check the codes, ask them not to clear the codes as anyone diagnosing this will need those codes.