I have a 3500 express cargo I have had the torque convertor replaced at 45000 miles. No issues since besides a cracked fly wheel. Until now . I have 75000 miles now and when I hit bumps my speedometer drops and trans seems to slip. Only when I hit bumps. Roads have been wet when I've noticed. Not sure what it could be. Getting worried I am self employed and use this van every day and have fixed equipment in it I can't work without. Anyone else with thoughts please thanks !