when you say "switched out old card with new one" i assume you ordered it from cat and provided all the information on the truck when ordering? Model, serial number, old ecu number etc?
These ecu's are generally programmed by the factory based on your serial number build. If you just grabbed one out of another truck or just ordered one out of the manual and threw in on the truck that's probably not going to work.
As for the com errors you must have some plug connection issues at the ecu or somewhere on the truck. I'd check the relay box's also and make sure those connections are clean, both box's, not just the one under the hood.
btw... what is the serial number of this truck?
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