Help with an overheating issue?

I have a 2001 Firebird with approx. 105k miles. It gave no indication of a problem and everything was fine until tonight on my way home from work. My check gauges came on and the gauge was pegged at 260. I had just looked at it a couple minutes earlier and everything was good. It gave no indication anything was wrong. No running warmer than normal, just nothing out of the ordinary in general. I am baffled because I regularly check my car and it was good on coolant on last check. I had replaced the thermostat about 2-3 years ago when it started running a little warmer than norm. I am going to replace the thermastat and the main radiator hoses tomorrow along with making sure it has plenty of coolant. What could possibly be wrong with my baby? This is my daily driver and I cannot afford to have it down. Thanks in advance!