It might be the valves but if you're using the ones that came w/ the wheels that's doubtful. You might be over tightening them, but doubtful. How was the hole made in the TL tape? I ALWAYS use a hot spoke to make the hole, this way the tape never splits and causes leaks. I NEVER poke the hole w/ the valve head or anything other than a hot spoke. I have fixed numerous leaking wheels by re-taping and doing this.
And the other thing...I hate road TL. As much as it's the only way to go for mountain bikes I will never ride it on the road again. One damaged tire years ago was all it took. What a mess.