Welcome, I am Chris (aka-Moose)
The flashing tow/haul light is most likely because the PCM does not know the vehicle speed, so it does not know how to control the shifts.
The solid on CEL light is most likely a 0500 VSS vehicle speed sensor code.
On this vehicle the speed signal comes from the ABS module. Do you have a scan tool to monitor it to see if its registering a speed signal? As well to see if there are unrelated codes, which can indicate electrical interference effecting the speed signal?
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