Overcooking is the main reason your pudding could be lumpy. This is egg curdling. If you catch it early enough, you can strain your pudding through a fine mesh strainer. Taste the pudding; if it has an eggy taste, there is no saving it. If you see it curdling before you add your caramel, just trust your instincts and start over. This way, you won’t have to remake the caramel as well.