Transmission issues

I bought the car listed above (it is the zx2 model) about three weeks ago. I have not had the money to get the fluids flushed and changed yet being that paid day is every two weeks, anyway the other night the car started to revved really high while I was driving. it only seems to happen once I hit third gear and once I get going the rpm's drop back to one. can I just flush it and will that fix it or am I going have to start looking for a new transmission? I bought all the stuff to do a transmission flush myself I am just really hoping that will fix the problem. any insight would be greatly appreciated.