1997 5.9 Backfiring out of exhaust after new cat.

Engine Mechanical problem
1997 Dodge Ram V8 5.9 Four Wheel Drive Automatic

Replaced Cat two years ago. Last week went to start the truck it would not start, it would turn over but not start. The cat was clogged again, replaced it and new muffler. The truck started drove for 12 miles started backfiring through the exhaust, just would not go. I pulled over reset the comp and it drove another 10 miles almost home then started the same thing real bad. The truck always has a anti freeze smell to it but it doesnt run hot at all stays right around 180, not that it has anything to do with my problem. Can anyone point me in the right direction to start. Will a scanner pick up a code if the cel is not on? I cant afford to start replacing things if there not bad and so many sensors not sure where to start, any help would be so appreciated.
Thanks
Stacey