It starts. When you drive you have to force the gas pedal down to get it to go over 55 and it shudders. Then it shudders and gets worse to the point where we thought we were never going to get home with it. My husband had to keep his foot on the brake and the pedal when the traffic slows down as we were afraid it would stop. It, of course has a throttlebody carbueretor.
If you have to stand on the gas pedal to get it going and then it shudders, I tend to think there may be an engine mount problem.
You might want to check for a resistance in the exhaust system. Such as a plugged catalytic converter.
Tester
I think you mean Throttle Body Injection and GM was way past TBI in 2000. Lets us know why you included “of course it has a throttlebody(sic) carburetor” in your post. Has the fuel injection type been modified?
Tells us about check engine lights and maintiance. Are you saying the accelerator pedal requires extreme effort to depress?. Have you looked at what is causing this resistance?
You could also end up with a bad engine control computer. This is never a common problem, but if you keep getting different codes or no codes at all, it might be a problem. When bad shuddering happens, I always get reminded of computer problems. Did you get fast idle too?
I think something is lost in translation here. True, it has a throttlebody but maybe the OP thinks this is actually a carburetor.
Knowing the mileage, maintenance history (if any) and if the Check Engine Light is on would help. (No doubt the CEL is on)
Severe engine miss, failing fuel pump, clogged converter, etc. are all possibilities.
If it starts and apparently runs fine before the sluggishness and shuddering start then I’m also leaning towards a converter problem.
Continuing to drive the car in this condition only makes the situation worse and causes even more problems.