It has no power. there is no ch. engine light. the cat converters appear to be o k. ignition wise its seems fine. not a gas problem. what else could it be?

It's losing power going up hills because the vehicles catalytic converter is plugged ,because it's running rich . Too much gas going into the cat . You need to have fix before your check engine light comes on an you have a code P0420 and or a P0430 catalytic converter efficiency . Well i guess it doesn't matter the cat is bad already . Can cost up to a grand .

More detail would help, such as what are you working on, and fuller description of symptoms. If you are saying that as the engine revs, power seems to drop off, there are many possibilities. Clogged exhaust system (think bad cat converter), or bad ignition module (they have a low speed section and a high speed section), inadequate fuel delivery, gas pedal not opening throttle all the way, or if your vehicle is "fly-by wire", bad gas pedal section.

code p 0420 refers to cat converter system bank 1---efficiency below threshold====causes ---cat converter---wiring---HO2S (heated oxygen sensor, the one in the exhaust manifold before the cat converter)
code p 0300 is random misfires
I would suggest changing the HO2S as it reports to the ECM on exhaust content so that the ECM can adjust the air/fuel ratio
so it is logical that if that unit is not reporting correctly, the cat converter may be having trouble burning off the gasses correctly
The oxygen sensor(O2S) reads the results of the cat converter operation and helps fine tune the ECM settings

SOUND LIKE LOW COMPRESSION.EXCESSIVE CARBON INSIDE ENGINE CAUSE ENGINE TO DIESELING KEEP RUNNING MAKE A RATTLING NOISE WHEN YOU TURN OFF IGNITION.

the code for gas cap? is also a code for small leak in evap system which includes the fuel /vent lines and canister check that the lines weren't damaged when cat was put in also check coolant sensor in reservoir connections runs by exhaust system

This could be anything from an ignition issue to a clogged catalytic converter. If the converter is clogged you may have a fueling issue that caused it to break down prematurely. This would have to be addressed before replacing the cat that is if the cat is plugged. Now if you have an ignition issue this also could cause the cat to deteriorate quicker. Either way it sounds like your going to have to have a professional look at it. Now if your lucky it may just be a bad sensor. But the question is which one. Again this is money wisely spend if you leave this to a professional.

you have a cloged cat converter, or an exhaust leak near the manifold... if you rev it at idle and it sounds loud check under car for loudness, if your driving and your going about 30 and it sounds like 90, its the cat converter, replace is the only fix for converters

Check the 02 sensor and the ignition switc.

Had the same codes on my truck. cat converter was plugged. I was told to take the cat off and gut it, then put it back on and it would run fine, but that didn't work. You need a new cat. Might want to replace the o2 sensors before and after the cat also. Hope this helps.