Why large speed difference between TKIP and AES encryption?

I was playing around with my wireless router settings and I noticed something strange.

When I set my computer to use AES encryption, my link connection speed became greater than 54 Mbps. Unfortunately, running some internet speed tests showed a consistent download speed of less than 400 kbps, although my upload stayed around normal at 4000 kbps.

When I switched to TKIP encryption, my link connection slowed down to 54 Mbps (which I'm assuming means it switched to G mode rather than N). However, my speed tests resumed their normal fast speed of downloading at 10,000 kbps or higher, and upload around the same 4000 kbps range.

I'm trying to figure out why the heck this would happen? Is this a problem with my wireless card? A problem with my wireless router? Has anybody seen anything like this before?

Thanks.

i have never seen.. normally would recommend aes because it is a much more secure. Whenever you enable security on a wireless network you take some kind of performance hit (security requires extra bandwidth and processing time). Maybe your router did not ship with aes and it was part of a firmware upgrade and aes is to much math for the router??

when you did speed test was it to the same site? and you did it a few times?

I've now tested it on 2 laptops to confirm it is not a problem with my wireless card. Whether it is a problem with my router or not I have no idea but I am suspecting the answer is yes.