I have to say, I'm right with 311 on the frequency thing. And remember, an upper/lower split is not necessarily harder. You're trading volume for frequency.

I actually find it much easier and somewhat liberating to train all muscle groups several times a week at a lower volume than to train them once at high volume. Its a lot less boring, and, I don't know, about a hundred times more effective.

If your building up fatique in some kind of cycle, there obviously may come a point where you're going to be rundown, but, personally. I'd rather become exhausted after a whole bunch of productive workouts than just a few (that may be less productive).

I'm not saying that some high volume work on lagging body parts is not beneficial. But even then I think increasing the frequency on those body parts even more while keeping the rest of your program the same will probably work better.

I'd give what 311 has suggested a good try, much longer than a week. I find I really LIKE high frequency training, whereas I hate high volume training because I used to work my ass off for very little return.