This happened twice - going about 65/70 mph and car suddenly loses acceleration. Pressing on the accelerator will very barely give you any pickup speed down to about 40 mph and that's all I can reach. Pull over to find what I believe the manifold to be glowing red.

First time this happened the mechanic cleaned out the cat, seemed to be working fine after that but then it happened again.

After you let the car sit for about 45> mins it will run fine for a while...

Car does burn oil but not even a quart every 2000 miles.

Any advice or suggestions would be great.

Here is an image:

 

I'm thinkinig a bad cat and that O2 sensor might be fried from the extreme heat. Replace cat or run a straight pipe in its place for a test.

I'm not a mech,maybe some others will share their thoughts.

 

Thats your exhaust mani. The car doesn't overheat? Thats extreme temperatures for those headers to be getting that hot. Never seen this before. Someone will help you figure it out though.

 

Did the CEL come on? Does the CEL work (light up for the bulb test if you turn key on but don't start)? It's a combined manifold / cat. A rich run or misfiring will overheat the cat. If it melts down inside, "cleaning it out" can't be done other than removing the now melted active material, which is highly illegal since it will no longer remove pollution.

 

@B18boosted: There is no indication that the car is overheating.

The CEL does come on. Also, if I let the car sit for an hour or two it will run fine afterwards (not sure for how though because I haven't risked it)

How much would a combined manifold / cat. cost? I've gotten one quote that the part would cost 499.

I've had it scanned at Autozone and these are the codes returned:
Troubleshooting P0420

Definition
aa Catalyst system efficiency below threshold bank 1
Probable cause
aa1. - A/F ration concern
aa2. - air leak near HO2S (heated oxygen sensor) Bank 1
aa3. - Ignition system concern
aa4. - Faulty catalytic converter

Troubleshooting P1298

Definition
aa Electric load detector (ELD) circuit high input
Probable cause
aa1. - open or short circuit condition
aa2. - falied ECM

Troubleshooting P0135

Definition
aa A/F sensor 1 heater system malfunction
Probable cause
aa1. - open or short circuit condition
aa2. - poor electrical connection
aa3. - faulty a/f sensor 1

 

This probably starts from the primary O2 sensor and code 135. Engine cold, unplug sensor 1 (the one on top, before the cat) and measure its heater resistance between the two wires that are the same color. Should be 10 to 40 ohms I think. If open circuit, replace sensor. If sensor resistance is OK, plug sensor back in, turn key on but don't start, then measure for battery voltage on the black and yellow wire going to the sensor.

ELD codes are often spurious. Ignore that for now.

If the cat has been burnt out or hollowed out you will get code 420. But the primary sensor has to be working first.