Another NL question

[Baby Mantis]

I just posted a question about whether I should start playing Limit vs. NL.

I was just pondering another question though regarding my play in SNGs and MTTs, all NL.

I have done well in SNGs, cashing around 35-40% of the time. I might add though that my heads up play needs a lot of work. Because I have only won a few heads up matches, and have came in 2nd or 3rd a lot.

In MTTs on the other hand I cash may 15% of the time and the best I have done is 12th. I have never made it to a NL mtt final table.

Now my question is what is it that is holding me back in mtts but not sngs. Is there anything that you guys do in each that help. Any suggestions are greatly appreciated.

I might add it is all NL holdem I have been playing.