This is going to get long so hang on to your chair.
Chicubs is right, not to run smack about your game, but your admitted 40th percentile finishes in your tournaments is not a huge deal. Consider some very randome assumptions on my part. Probably a good 15% of people who enter the tournaments you're playing can safely be considered "dead money" meaning their chances of winning or placing in the money are virtually nil. I see that 15% as being a fairly lowball estimate of the "dead money" in the tournament. When taking this into consideration, your 40th percentile finish is actually diminished in that you're probably only besting about 25% of the actual players in the tourney that have a decent chance at a money finish, final table appearance, or win.
From the situation you describe, it sounds to me like you have tightened your play so much so that you're preventing yourself from having a large enough stack in the middle to late levels from which to work with. You must attempt to capitalize on every single opportunity presented where you can increase your stack while not putting your tournament life at stake. Try to avoid "race" type situations as much as possible as it usually isn't as necessary as some like to play it. During the early stages of the tournament, aside from the donks that go out on the all-in festivals during the first few orbits, players tend to be fairly tight, and playing almost strictly premium hands is the best way to go. During this time bottom set or bottom two pair isn't going to get you there in most cases, but as the game progresses, you simplt must loosen up a little and slightly adjust your starting hand requirements in order to keep up with the blind structure. Also, make sure you're not letting your blinds be stolen to often. The blind protection is imperative at all stages of the tournament but as with everything increases during the later stages incrementally with the size of the blinds and antes.
I'm not sure how you're playing exactly, but limping into pots from any early position is usually not a great move to make as you're making yourself voulnerable to a raise behind you which is going to leave you not knowing where you stand in the hand. Keep in mind that when you're up against one or two players in a pot as the tournament progresses and you miss the flop, there is a chance that it missed your opponent as well and a lot of times with a decent starting hand you can take a pot down with a raise. This strategy isn't something to make a habit of, but one that will work in many instances. All the above advice comes back to the capitalization of as many situations as possible that present themselves upon which you can increase your chipstack.
Very often there will be orphan pots that people will pick up with virtually no hand because they have the balls to fire at them after missing a draw. Why give this money away to someone else when you can be the one to rake the pot uncontested.
The most important thing, in my estimation, to remember is to make sure you're able to adjust to the constant changes in situations during a tournament, but don't place so much emphasis on it that you play in a manner that is uncomfortable to you or that puts you in danger of making maniacal moves that send you to the rail. I'm sure much of this seemed like rambling, but it is basically a stream of conciousness that you can take some pointers away from. Good luck.