So I know this topic has been talked about a thousand times before, but I'm hoping everyone will cut me some slack anway.

On rides over 5 miles in length, I get numbness in the outside of both feet. I don't seem to have it anywhere else, and I'm not sure what is causing it. Taking a break from pedaling for a bit seems to help, but only one foot will recover at a time (recovery seems to be dependant on position within the circle).

I'm riding clipless with moutain shoes... ie, not very stiff.
I never notice this on rides less than 5 miles (regular shorts, not padded), but definitely on longer rides (padded shorts).

I don't know what else might be relevant....

Any suggestions on what is causing this and how to eliminate it?