Well, I think a lot of times we hold back on the bike to save it for the run.

The key to getting over that hump... is train like ya race. Meaning... go out and ride all out for 15-30 miles in training and then do a 3 mile run. See how it goes. If you know you can do it in training, then you won't be holding back on race day.

You can also experiment with a "C" race. Pick a race that you don't care about... and go out there and just race all out. See how it goes. If you fall apart on the run and have to walk, then so be it... it's not a race you care about anyways.

I did this on one of my "C" races this year and learned that pushing it on the swim and bike didn't affect my run. I was still able to hold the average I wanted to on the run without dying. Then again, I also trained that way too... since I try to do at least 1, 30/3 brick weekly.