2000 V6 Rocking Accel with Less Than 1/4 Tank of Gas

I've got 55,000 miles on my truck and about 2 tanks of gas ago I started having a problem whenever I accelerate with less than a quarter tank of gas. The truck rocks real bad and on occasion (10% of the time) it takes three or four tries to start. I fill it with gas and my problems are solved. I've changed the fuel filter and even ran the tank empty in case it was bad gas. One thing I thought of, but have no idea how to do is change the fuel pressure regulator. Is this an easy task (I am by no means an avid mechanic). Would this possibly solve my problem?

Thanks in advance.

I have seen this once before and the truck came in full of gas so we knew it ran fine full. We drained the gas tank down to 1/4 tank and then drove it and it surged quite heavily under acceleration. It was not getting the proper supply of fuel, we replaced the fuel pump assembly and it ran fine. The fuel pump is a module assembly in the gas tank. Good Luck.