Send me all your '10 105 stuff, and I'll pack up all my 2008 and send it to you. Mine works fine.

Seriously though, I remember my FD/shifter being a little stiff at first, like I had to force it sometimes. It got better. I do recommend learning about adjusting your derailleurs and working on it yourself.

Can you describe what you mean by "slipping/not shifting"? Do you mean, gets 1/2 way into a shift and hops in and out of that position noisily? Maybe you're not pushing the lever all the way? (It's kind of a long throw IMO.)

Don't feel jipped about getting some 09 parts on a 10 build unless there has been a useful/important change in that model line. I don't know any difference between 09 and 10 105 shifters, and I haven't heard anything about 09 ones having problems. (Not that I'd know for any reason other than people would ***** endlessly about it here.)