73 Cadillac deville, runs good at low rpm but when you step on it, it runs rough and has no power. I have done a tune up with plugs, points and replaced fuel pump. What next?

Check the catalytic converter. If it's plugged you will have similar symptoms.

Your fuel line from the tank to the fuel pump may have a small hole in it. Then your fuel pump would be pulling some air into the fuel line, giving poor performance under load.

I checked fuel line for small holes, it is OK. How do you check to see if catalytic convertor is plugged? Do you have to take it off to check it?

Usually when cat is plugged the exhaust has a hissing noise instead of a rumble.

I would try to run a temporary rubber fuel line to the fuel pump, and see how it runs. I suppose you have a new fuel filter. If it is carburetor-ed, the carburetors' jets could be plugged. If the cat is possibly plugged you would have to remove it, to see.

There is no cat on this car. Thanks for the ideas tonythe woodsman and aztec626bf. What next? I'm guessing it must be in the carb, which is a quadrejet. I am reluctant to tear into it as they are a complicated carb.

If you go to the Carburetor Exchange you can get a kit and they supply a very helpful schematic with the kits.

i have the carb kit ordered, will try that next.

i finally found the problem! It had a double walled exhaust pipe from the y-pipe to the muffler, the interior wall had collapsed. Installing a new exhaust pipe did the trick. It now runs great.