NAVIGON APP very slow. help please!!!

Hi, I have bought the navigon app, but it is very slow everytime i use it. Slow start up, takes a long time to respond to any of the touches, and rerouting is slow also. Is anybody experiencing the same problems?
What should i do? I have had before the real navigon gps device, until last week when smbdy stole it from me. I bought the app hoping i could save some money and be able to get around. BUT THE APP ***** BIG TIME. By the time i put the address in and get the GPS signal, I am already at my destination.

What can i do. Can you pls help me? Do you thing i could get some sort of refund or store credit with iTunes?

Sorry, just n iphone beginner here.

Thanks and good luck.