Stalling under 1000 rpms doesn't sound like fuel pressure or Cat to me.

Under 1000 rpms is when you need the least fuel or exhaust flow.

Sounds to me like a vacuum leak, problems with the idle air control valve, or possibly a bad O2 or MAP sensor.

1. Check for codes. I have people say there were no codes because the check engine light was burned out.
2. Look for obvious vacuum leaks. If it is a Magnum engine ram check for oil in the intake by looking through the open throttle blades. A common vacuum leak is when the intake pan gasket fails but it usually includes a little smoking.

3. Then start checking for Fuel Pressure, CAT back pressure, etc.

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Hope it helps.