If I texture, say, grass as a floor of a program, and that is the only thing drawn, why would my walking function (which works fine without texturing) work fast at first, then slow to a crawl as I am walking on the texture? Is this hardware issues, or is there something that I can fix in the code? Thanks.

This seems strange, perhaps you draw more and more?

One unlikely suggestion is that the repeating texture coordinates get larger, but really tha seems unlikely, these things get normalized internally. Make sure you don’t draw the ground as one massive big quad, split it up into several textured quads, otherwise you may be seeing massive texture coords causing issues. This is a bit of a wlid guess, but there’s not a lot to go on.