Nissan Repair: Truck Missing, nissan frontier, advance auto parts

Question
I have a 1999 Nissan Frontier 4x4 with a v-6 engine automatic transmission.  I recently purchased a full tank of gas and drove about 1 mile and the truck started missing.  I probably drove another 50 miles and the miss got more severe until finally the truck would hardly run.  When I would spot at a light i would have to kick it into neutral and hold the accelerator down a little to keep it running.  When the light would change I would place the transmission in gear and the truck would miss fire so bad I could hardly get through the light and it would take a long time to get up enough speed to stay out of everyone's way.  I finally made it to Advance Auto Parts and they checked with a code reader and it said Knock Sensor.  I made it to a garage and they replaced the fuel filter and it ran much better, they said the fuel filter was blocked up badly.  I used some chemical to take water out of fuel just in case it was fuel with water problem.  Doesn't seem to make much difference.  While it is running much better after the filter change it is still missing.  However, it does not miss as bad when the engine is cold as it does after it warms up. I have had a lot of suggestions from friends from fuel pump to spark plugs.  I should tell you that the spark plugs and plug wires are only about 3 months old.  I feel like I must have gotten bad fuel but I don't know what to do and I don't want to start changing parts.  The garage said if the fuel filter didn't help they wanted to tune it up and if that didn't help they would try something else.  It is said but it appears the mechanic is just a change a part and if that doesn't work change another.  I could win up with a lot of money in repairs I don't need.  I change the sparkplugs today, removed the gas tank and emptied it out.  I filled with new premium fuel and installed another new filter.  I captured a gallon glass container of the old fuel and after it sit for awhile there was about a 1/2 to 3/4 inch of water in the bottome of the glass container.  After refilling the tank my truck ran better for about a mile or so and started missing bad again.  It might run a 1/2 mile without missing then will miss and jerk for a little ways and smooth out again.  I have been told to change the filter again. Could you please estimate how many time I can expect to change the filter and how long it will take to get all the water out of the system.  Am I on the right track or is there something else I am missing. Please any advise would be appreciated.

Answer
Hi Billy -

Have you drained your fuel tank?

The only way you can be assured of proper performance after your ordeal is to completely drain the fuel tank. What you captured in the gallon container is just a smalll sample of what is going on in your tank. There are a lot of baffles in the fuel tank and it is not possible to get all the fuel out with siphoning, or with it on the truck.

PLease get back to me and let me know -

BTW, is there any way that you can take that gas back to the place you purchased the fuel from and demand that they be responsible? I am sure it happened to many others and by now they should be aware of their mistake.

Let me know, now -
aloha
calvin