[Knifeblade]

check the reverse linkage arm for full travel to engage the pawl. A possible is the small mechanism in the shift console, under the shift console plate, is not fully engaging, and allowing the shifter arm to release. This mechanism has plastic parts, which wear, sigh. The catch sometimes can't engage the reverse lever-arm fully once worn, and will pop back out. "Slamming" just accelearates the wear.