Warm engine stall shifting from drive to reverse

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2009 Chevy Express 2500 6.0L 4L60-E Trans - 95,000 miles What would cause engine RPM to drop and eventually stall when shifting from drive into reverse? When engine is cold shifting from drive to reverse is fine. After 30 mins of driving and engine warms up shifting from drive into reverse stalls engine. Shifting from any other gear to reverse NO stall. MIL is off. No DTCs on scan tool.