My 2020 Laramie did it with a bed full of Xmas gifts, and the dash doesn't give you a warning. FCA disabled the tailgate alert in most RAMs, except the Limited.
FCA was getting too many complaints about false tailgate warnings, so they just disabled it in the software. Your truck probably has everything to get an alert when it opens unexpectedly. Search Alpha ODB to re-enable the warning in the software
FCA needs to address the tailgates opening or the alert. Having neither is ridiculous for a truck that costs so much.
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