Loss of power

After having my 2002 Grand Prix GT repaired from Blown intake manifold gasket, I've noticed that after start up I have now power from a stand still. I disconnected the EGR Valve and got some power. Could my Cat be clogged or should I look for something else wrong?

yes, your cat could very well be clogged. Antifreeze is the number one killer of catalytic converters, and the 01-02 Grand Prix's also have a known issue with the cats being bad from the factory. GM issued an extended warranty on the converters on 01-02 GP's (check the tips and maintenance sub-section at the top of the GP forums for more info) due to an issue with the substrate breaking off and blocking exhaust flow.