2005 GT: Questions About P0193 Code?

Hey guys, I had a couple questions regarding the P0193 Code that my Mustang has started throwing this weekend. Last Friday, my CEL came on and I went to my local auto store to have them read the code, and they came back saying they didn't know what it was but it was the P0193 and cleared it. Then this past Sunday, the light came on again and I went to a different auto store, and they told me again it was the P0193 Code--which stated that the Fuel Rail Pressure Sensor was reading fuel pressure levels higher than acceptable. I have done quite a bit of reading online about the code, and everything seems to suggest to replace the Fuel Rail Pressure Sensor. However, the people at the auto parts store said that their computers recommended replacing the Fuel Tank Pressure Sensor (NOT the Fuel Rail Pressure Sensor), which is located on top of the fuel tank. Nothing I have read online suggests that this is the problem area for this code, and I have not bought either sensor yet as I am trying to pinpoint the problem. I have removed the vacuum line on the FRPS and visually checked it on and no gas has gotten through, but I understand that visuals alone cannot tell whether a sensor has gone bad.
I will be honest and say that I have no clue how to access the sensor on the fuel tank. Can I access it under the back seats? Do I have to drop the tank altogether? Is it the problem in the first place?? A diagram would help tremendously if someone has one and that is the case! I am assuming that since the fuel pressure is reading high, the fuel pump is still capable of sending fuel at a sufficient rate, and thus the pump is not the problem (as opposed to the fuel pressure being low). Anyhow, I am not sure what exactly is the specific problem.
I will note: this light came on before a 500 mile round trip this weekend when they cleared it, and came back on with about 150 miles to go(I drove about 350 miles before the light came on once again). I have had ZERO problems with the way my car is running, start ups, acceleration, deceleration, or anything else regarding the drivablilty of the car! That is what is confusing me, but since the light has come on twice in two days, I am fairly positive that something is indeed wrong. Any help, comments, or replies will be greatly appreciated! Thanks so much for your time!