I have a 2000 seibring convertable that stopped running one day so I took it the dealership and they told me it was sparks plugs well 700 dollars later they couldnt fix it so I towed it home and I got it to start but it hesitates when you try to go from a dead stop untill the RPM's get over 2500. When its cold it runs fine but once it warms up I start having this problem. I have replaced the fuel pump, Wires, Plugs, Cap, Roter, intake manifold gasket, catilic converter, I still cant figure out what is wrong.

 

There have been several similar postings here on this forum. It usually turns out to be the distributor including the camshaft position sensor. You have to replace the whole distributor. Before you go spending that kind of money you might want to check for fault codes in the engine computer.