Just Can't Figure It Out?

98 C1500 w/Rebuilt 5.7 and new MFI. Throwing codes P0420 and
P0430 after trip to the dealer to solve a dieing issue. When they first drove it they only got a code for a loose ground. Somehow on their second test drive the Crank Position Sensor went out causing it to run like c*** above 30 mph. When they checked it no other codes showed up other then the one for the CPS. These codes popped up the next day after I let it warm up a bit, took off down the road and stopped at the first sign. Thing runs like a champ and I have zero starting issues. Does smell a little rich out of the pipe though.

1) I have no other codes.
2) Could the heavy misfiring have killed the cats?
3) Dealer checked fuel presure said around 60, but could I have done something to the fuel system while running the fuel pump off of the test lead under the hood?
4) Tried to test the Coolant Temp. Sensor and it was very hard to get a good connection with the probes but I finally did. At ambiant tempurature I got 1950.
5) If there was anything else "broke" would I not get other codes?

Thanks, this is killing me. What should be a good experience is turning real bad.

98 C1500 w/Rebuilt 5.7 and new MFI. Throwing codes P0420 and
P0430 after trip to the dealer to solve a dieing issue. When they first drove it they only got a code for a loose ground. Somehow on their second test drive the Crank Position Sensor went out causing it to run like c*** above 30 mph. When they checked it no other codes showed up other then the one for the CPS. These codes popped up the next day after I let it warm up a bit, took off down the road and stopped at the first sign. Thing runs like a champ and I have zero starting issues. Does smell a little rich out of the pipe though.

1) I have no other codes.
2) Could the heavy misfiring have killed the cats?
3) Dealer checked fuel presure said around 60, but could I have done something to the fuel system while running the fuel pump off of the test lead under the hood?
4) Tried to test the Coolant Temp. Sensor and it was very hard to get a good connection with the probes but I finally did. At ambiant tempurature I got 1950.
5) If there was anything else "broke" would I not get other codes?

Thanks, this is killing me. What should be a good experience is turning real bad.

with the excessive missfiring the cat converters may be damaged,coated with carbon deposits...this would cause this / these codes to occur...this vehicle is very fast to throw these codes when the cat converters get weak...

it is possible to use an additive that claims to remove these deposits..I would give it a try and after a couple hundred miles it may work out..

how many miles on this vehicle[not engine] ?

Have 163,500 miles total with only 40 on new motor. Just can't figure why they went out now, or if they are the real problem.

Have 163,500 miles total with only 40 on new motor. Just can't figure why they went out now, or if they are the real problem.

the miss firing if severe and prolonged,,can very easily contaminate the engine oil...if the oil smells of fuel change the oil/filter..