No power PLEASE HELP

I have a 2001 grand prix gt 3.8 N/S. It has 162375 miles. Heres the problem i was driving on the highway and the car would not go above 65 the rpms would rev up and nothing . Took it to the trans sho. No codes they say its a engine problem. Know the car will not go past 35-40 mph like i said no codes no lights this happened almost instantly. Its going to the shop i was just looking for ideas. I unpluged the MASS air FLow sensor still same problem Just replaced all the plugs and wires last month and the car has been running great it idles fine still but has no power past what i said. I was thinking maybee a clogged cat converter but i dont think it would happen almost instantly like it did. Any help would be appreciate. Also tranny fluid good, oil good just changed it. :banghead:

Do you still have the original (OE) converter? Its possible. Get it tested via a back pressure test or engine vacuum check.

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Click here (http://www.automotiveforums.com/vbulletin/showthread.php?t=681283)

The checked the CAT its not clogged any other ideas im open

Open radiator with engine cold and check coolant. The vehicle will attempt to protect itself if it believes an overheat is occurring.

If the radiator is full, the next place I'd look is the fuel pump. If I were in your shoes and planning to keep the vehicle longer, I'd just replace it if it has not yet been done.

Do the RPM's go up and vehicle not move? Or when your driving and hit the gas do you feel more like hitting a brick wall, pedal to the metal, rpm's low, and car just creeps along?