net slow down

I have set up a tp-link wireless N router with my laptop and 2 notbooks.(both old ones) I use linksys g pci adapters and get a great signal. But after starting a download or even loading a large page my transfer speed starts dropping till it hits 1 mps and wont load a page. Sometimes with out doing any thing it goes up and down. I have recycled my router, changed channels(1 seems to work best.) I am measuring speed by the linksys program in case your wondering. It starts at 54 mps and drops to 1 mps. When it says 54mps the laptops fly. I also tryed opening band with from auto to max(40) If I rescan with my linksys program it goes back up to 54 for a while. I'm using wep 128 encription. My cable connection remains steady. Any ideas?