I also struggle a lot with T and D. I found a hack that works for me, I wish it works for you as well. For example you want to Tom, dont start with T (where your tongue touches your top of your mouth) rather start with your mouth in the 'E' position and pronounce it has IT-OM (ITOM) . Of course people will say why you pronounce it differently. Dont worry it never enough for them. Good luck!