Training for the 4000km pursuit?

Hi
I am new enough to track racing and I plan to concentrate on the 4km for the next year with the aim of next years world cup. my best time is 4.45 and I seem to have hit a brick wall with regard to improving. Flying 2k is an equally week 2.16. My idea is to improve this 2km time by using 5min SE on hills comlemented with 30sec on 30sec off x 15 min twice on ergo trainer. Am I barking up the wrong tree, should I be focusing on LT ie 3x20min or does the body just respond to specific training adaptions ie 8x4min (this is where I have hit the brick wall with training)!
Any thoughts are appreciated!