Engine light flashing

O2 may still be getting readings out of limits, This could be related to the same reason cats clogged with is running rich. I would b4 replacing o2's check the normal items like plugs & wires, Air filter, clean MAF with CRC MAF cleaner & throttle body and IACV, TPS with CRC Throttle body cleaner and will need new gaskets on the IACV & Throttle Body, Make sure there is not any arcing with plugs & wires Can us Dielectric grease between boot & plug and same on boot to coils. Be sure not to touch the MAF filaments wire they are easy to damage just spray them off. i would also see if those codes are set and can erase them.

Here below is a test for down stream o2 sensor testing which is the 2 past the cats.

http://troubleshootmyvehicle.com/gm/4.8L-5.3L-6.0/diagnosing-codes-P0141-P0161-page-1

Here is the upstream test page below, copy &past see if these test match for you truck.

http://troubleshootmyvehicle.com/gm/4.8L-5.3L-6.0L/P0135-P0155-diagnostic-tests-1

This site has many other test for most auto's so you can search it to find others too.

Thank you I will look into those sites

So figured out its not the coil or plug . We swapped cylinder one and 3 and got same result . Code still reads cylinder 1 misfire

Mine is doing same but says 3 and 4 im stumped