contrarian i have had same problem as you and ive played a lot of mtts, i often have found myself short on chips as tournament gets to late stages this is because partly im not three betting enough and trying to play value hands which doesnt work in tournaments most of time because the guys with big stacks are often playing a lot of pots and seem good at working out where they are in them.

If you ever watch a replay of a final table of the sunday million you can see this in reality as often the guy with the huge stack like 70-80bbs is the one who is opening most of the pots and playing more aggresively and less probably bluffing more than others and the ones who are waiting for big hands to double are bleeding away and end up going out early in final table.

I did a little better at a few recent fts when i picked spots to three bet light using my tight nitty image to steal some pots and its amazing when you play nitty or tight players just fold to your three bets so often often snap folding because they think you always have it, so you have to three bet more and i guess do it in position when you can so if called you got better chance to win pot.

I have seen some guys who seem to have done well in mtts not playing real aggro but calling often in position with hands that flop well/ok and stationing aggressive players with a pair or so and winning big pots, i guess its important to rememeber that as blinds go up bluffing will increase and there will be more guys two /three barrelling air so by playing more pots vs these aggressive players maybe you can win a lot more chips but ive always been afraid of flatting hands like kj k10kq even in position late in tourny incase im dominated but these hands do win big pots sometimes by bluff catching.

anyway gl and when you start to get short i guess you need to get involved and dont worry about busting as we know in most mtts specially low buy in ones all  money is in top 3 so busting 13-14th or 20th doest matter at al.