Interference can be distance, and walls, or anything else in between. It can also be from other wireless devices such as phones, etc.
A lot more phones are using 5.8 GHz wireless, so you may have problems there as well.
If you are having trouble with signal strength as well, I recommend you use something to reflect the signal if need be, to get around corners, or to hit each of the corners in the home or wherever.
But, a good bet is that your 52 Mbps can't be sustained either because of distance from the router, or interference from other devices, or both!
If you have to go through multiple walls, plus have cordless phones, you'll surely have some issues. You'll have to slowly remove each of those problems to see what really causes it to go down.
If worse comes to worse, and IF you don't have any other clients, you *could try* to lock the transmission rate at the maximum speed, and see if it'll help.
I do not recommend this however as it can be detrimental as far as performance goes. You may receive signal degradation or lost packets and have lots of retransmits. May even cause lag. So, it's not necessarily a good idea, but also worth a try.