luvmy2004lxv6

I could sure use some help and advice on this problem. About 2 weeks ago my keyfob would not work, using any of the button,s when I arrived at work. At the end of the day, I tried it and it worked fine again. Had the exact same thing again a week later. The third time it happened, a couple days ago, it stopped for good. I had replaced the keyfob battery a year ago, when the range was getting less, but tried a new battery anyway....no luck.. I tried the other keyfob, which is virtually like new, came with the car, and I know worked and still nothing. I checked the battery voltage and even installed a new battery in that keyfob. Still nothing. I tried the programming with the key off and on and pressing buttons as outlined in the manual and online instructions and still nothing. I can lock and unlock the car manually with the key. The driver's door rocker lock switch works fine and will lock and unlock all the doors from inside the car. It seems to me it is not receiving the signal from the keyfob. If I understand what I've read in the forum and from the shop manual, there a multiplex control unit in the driver's door with an antenna and it receives the signal from the keyfob and in turn sends a signal via a wire to the multiplex control unit under the dash, which then opens/locks the doors, flashes lights, beeps horn, opens trunk, etc. Am I correct in my interpretation of how it works? Would it seem most likely that multiplex unit in the door is the problem, since the door switches work when I use the rocker switch internally? Any help and suggestions on something to check would be most appreciated.