Q: 04 Galant won't drive past 40mph. Jerks and shuts off on dead stops unless accelerated.

Car won't go past 40mph. Starts reving and jerks. Also engine shuts off on dead stops when I let go of the gas pedal. Turning the AC on makes it worse. I have codes PO301, 401, 421 & 431. I have been told to replace spark plugs, coil, 02 sensor and exhaust system. Costing somewhere north of $1200 which is about the same as the car's worth. Someone also advised to have the muffler cut off and have pipes welded on to save money on buying new ones. What can i get done to make the car give me just a year more without having to spend this much? Is the cutt off and weld method worth it? Is there anything i can do to fix the issues without replacing all parts mentioned above? Thankyou.

My car has 177000 miles.
My car has an automatic transmission.