QUOTE(DAS44 @ Dec 26 2011, 06:23 PM)

Might be worth your while to try some high gravity ARS (I used Texmaster Sudden Ti, but tweaked nullpomino would serve just as well). It forces you to stack flat, if you don't you're digging your own grave. At first you'll suck (I blew something awful for the longest time), but it'll come naturally after a while.
I hit the first torikan just as my interest in tetris began waning...
Anyways... that might help
As someone who has played an absolutely sh**load of TGM, I disagree with this, or at least the way you suggest.
Playing Ti modes doesn't help a great deal. You still have hold, three previews, and the things that kill you in 20G ARS aren't the things that will kill you in 0G SRS. It will teach you things, but not things that are necessarily transferable. Sure, it teaches you to stack flat, but that's not always the best way of stacking for 0G SRS.
On the other hand, I would recommend playing TAP - either Death or Master, because you have one preview and no hold. While this is actually further from typical Nullpo 40L, it teaches you proper stacking to a far greater extent because you don't have assistance if you make poor decisions.
Really though, you could achieve the same effect playing Nullpo with SRS and just remove hold and use fewer previews, and it won't require you to need to get to grips with how ARS rotation and 20G works, but will still put you in a situation where you need to rely more on proper stacking than the tools given to help you stack. Playing without hold, ghost piece or previews is the equivalent of weight training for Tetris, and when you add them back in you should find you improve quite a bit.
tl;dr - if all you care about is SRS 40L, then ignore TGM and just try playing with fewer previews and no hold.