The muffler is getting very hot and turning red and losing power.

Except that it happens only after and hour of running, I'd be looking at the flywheel key, but it sounds like you're on the right track ...Maybe the exhaust valve gets sticky or warps a bit when it gets too hot. If it isn't closing all the way, it would get hot and backfire. I'd also be sure the engine is clean and cooling as well as possible of course. Good luck!

Usually, a red manifold means that you have a lot of unburned fuel going into the exhaust stream. Most likely cause of this would be a cracked or warped exhaust valve or valve seat. A compression check of the engine cylinders can confirm a leaky valve quickly. Another possibility would be a blockage in the exhaust stream. Converters can break up and their parts can move through the exhaust and clog up the muffler. In theses cases, however, there is usually a significant loss of power on acceleration and often both the converter and exhaust manifold will get red hot.

Blocked muffler will cause extreme reduction in power. When you say red hot, do you mean it glows red or it is very hot and you will burn your hand on it? The latter is normal, you cannot touch an exhaust system within a minute of running. Cherry red sounds abnormal. Engines putting out maximum power can have glowing manifolds but not average power. Make sure the timing is correct and do not use gasoline with an octane rating that is too high. Higher octane fuel burns slower. If it is still burning when the exhaust valve opens, it will continue to burn in the manifold. Use the gasoline recommended in the owners manual.

Are you sure its the muffler....or is it the catalytic converter? It is not normal for wither to get cherry red - this usually means that you have raw fuel being burned in the exhaust stream. This is usually due to a burnt exhaust valve.

I would say your exhaust converter is worn out & blocking
the exhaust from getting out & since you continued to wonder ,
verses actually having the car tested,that you now have ruined the transmission

Not RED hot, no.
You may have a restriction or a timing problem.
Was it that hot before you replaced the exhaust parts ?

It is quite normal for the pipe/muffler connected to the engine exhaust port to get very hot, especially when the engine is working hard running at speed under load. During daylight it is usually not noticeable, but at night it will visibly glow up to a bright red.

You will need to fix the exhaust leak first, this may be the only problem but check the ignition timing as well, as it may have been bumped during cad installation,or may not have been timed correctly if points were one of the new parts mentioned. and may explain the lack of power.

Sounds like a mice in your muffler. Its stuck, stop using it, you'll be damaging the valve on the motor. Remove it and test it. Try to remove thing in, i know some people put it in the fireplace to turn it red and burn things (like mice) inside and open up things...

Well this could be in your timing. As cars get some miles on them the timing chain stretches therefore causing you car to lose alot of power.So you may want to have your timing set on this car. Also I had a taurus that had a bad torque converter, and it lost alot of power on hills and under loads, also when i gunned the gas pedal. so try the timing first. Hopefully you dont have a bad head gasket or a cracked head these symptoms you are describing are all signs of head gaskets or blown heads