You may have answered your own question. If the car isn't starting in 1st gear, you will not have much power. Has the check engine light come on? Also, have you checked the shifter linkage to make sure it is in drive and not 2nd? If it is in 2nd, it will start in that gear in this vehicle. It is ment to help you get out of snow by lessening the power to the tires.
FInally, if you don't feel it is a shifting problem, have you checked to make sure the catylatic converter isn't plugged?