You know, I wonder about that bud. You've been around here for maybe about a year, and I think you've been plugging both your books for close to 8 - 9 months. I think it may have hit the saturation point here. Its possible that everyone who wanted your book here at MR may have already bought it.
The author promotion thread is getting a little too big for its britches. I don't go more than two pages in once in a blue moon, plus I already bought your books when they first came out. So I don't think I'm in your target demographic anymore...
So, here's your solution: Write a new book!