I was gonna say it sounds like a vacuum leak, but if you replaced those hoses I don't know? 2 were cracked, are there only two to replace? Are you pumping the gas pedal when starting?
It's a far fetched thought, but when I had my 2k2 Sentra and the ECU crapped out, it would put the car into "safe mode" and not let it rev past 2k RPM's...also the idling would do the same thing (up down up down, etc) But the most noticable problem was the smell of the exhaust, it WREAKED of gas. The problem was the car was running far too rich; an air/fuel ratio issue.
Possible computer replacement??