What would cause a loss of power and flashing check engine light?

I would say seperate have you had the exhaust checked for excessive back pressure?

The bad engine miss fire and only being able to go 40 with a big loss of power?Makes me think plugged cat. Its best to take it to a exhaust shop to have the back pressure done or you will have to buy a back. Pressure tester and learn how to use it.

How does it run now?It doesnt blow out white smoke out the tail pipe while running does it?As far as cost it all depends if it is a plugged cat an how much they cost.

Alright so it acts up when hot?Usually when the cat gets clogged thats usually what happens.I would have the back pressure checked. Also when its acting up do you ever have to let up on the gas for it to shift up to the next higher gear.

A plugged cat usually doesn't set codes sometimes it triggers missfire codes.

You should start with a tune up, if you have worn out spark plugs it will misfire.

Here is a guide to help you with instructions below:

https://www.2carpros.com/articles/how-to-change-spark-plugs

Spark Plug Type .................... ZFR6F - 11G (NGK)

REMOVAL
Each individual spark plug is located under each ignition coil. Each individual ignition coil must be removed to gain access to each spark plug. Refer to Ignition Coil Removal/Installation.
1. Prior to removing ignition coil, spray compressed air around coil base at cylinder head.
2. Prior to removing the spark plug, spray compressed air into cylinder head opening. This will help prevent foreign material from entering combustion chamber.
3. Remove spark plug from cylinder head using a quality socket with a rubber or foam insert. Also check condition of ignition coil O-ring and replace as necessary
4. Inspect spark plug condition. Refer to Spark Plug Conditions.

INSTALLATION
Special care should be taken when installing spark plugs into the cylinder head spark plug wells. Be sure the plugs do not drop into the plug wells as electrodes can be damaged.

Always tighten spark plugs to the specified torque. Over tightening can cause distortion resulting in a change in the spark plug gap or a cracked porcelain insulator.
1. Start the spark plug into the cylinder head by hand to avoid cross threading.
2. Tighten spark plugs. Refer to torque specifications.
3. Before installing coil(s), check condition of coil O-ring and replace as necessary. To aid in coil Installation, apply silicone to coil O ring
4. Install ignition coil(s) Refer to Ignition Coil Removal/Installation