Flashing cel all of a sudden

I all of a sudden had flashing CDL light come on accompanied by low power and shaking idle. The flashing goes away when I rev it and let off. It will idle for a moment with out the rough idle shake. There is no knocking, ticking, smoke out of the exhaust.
When it initially came on drove it a couple miles to the shop.
That shop has recently (couple months)replaced all coil packs,plugs,wires, o2 sensors, radiator and thermostat ect,
They looked at it and small shop and were super busy, said all cylinders have little compression and feel the catalytic converter clogged and burnt the rings from back up and I need to replace the motor. it baffles me that all the said stuff was replaced and all of a sudden all cylinders leak and have no compression. The Rig starts sounds great minus the rough idle that will smooth out higher rpm’s or revving the engine fast feeding fuel and letting off, but only for a short period of time. Maf sensor looks great, throttle body inside has thick greasy oil build up. Oil smells rich, exaust smell rich no smoke. I even started it light was flashing, I put my hand over the tail pipe build pressure let off and light stopped flashing. Don’t know if that has any help diagnosing.
Anyone with any ideas? Would low voltage from shot battery cause this? It stays running after jump so alternator is working. Gunk in throttle body cause a failure somewhere with air/fuel mixture.
I know there is a plethora of things to check. But with a group hive knowledge, maybe a moment. Thanks if you read through my long rambling post!
cheers friends.

 

^Flashing CEL - constant misfire dumping unburned fuel into the exhaust. The flashing is to encourage you to fix it ASAP, else the unburned fuel will cook your catalytic converters shortly.

The shake comes from one or more cylinders not contributing, so the engine is out of balance when running.

Take it to another shop that has the expertise to do proper diagnosis, read codes, look at live OBD2 data, etc. At the very least identify the misfiring cylinder(s), confirm the ignition coil on that cylinder is getting a signal. Maybe mice chewed wires. Maybe the ignition coil installed by the previous shop went bad. Maybe the spark plug was counterfeit...