GA /t,d/ are usually alveolar, while AN /t,d/ are typically denti-alveolar. While for GA /t,d/ the tip and blade of the tongue articulate with the area immediately behind the upper front teeth without touching them, the contact for Dutch /t,d/ is generally further forward: the tip touches the inside of the upper teeth and the blade touches a larger area of the alveolar ridge. In producing an alveolar stop, ry to make a conscious effort to place the tip of the tongue slightly further back than in Dutch. When aspirated, GA /t/ is frequently released slowly so that weak friction is produced, so try to pronounce a weak [s] as you release the /t/: [tˢ].
The actual place of articulation of GA /t,d/ as well as the other alveolars /n,l/ may vary a lot under the influence of neighboring sounds. Before /r/, GA /t,d/ are post-alveolar, as in Try Dry! They are dental before, and sometimes after, a dental consonant, as in eighth, width, bathtub. Here are some examples to practice the main allophones of GA /t,d/.
[tʰ] tea, tool, latex, return, eighteen, intend, syntax, veto
[t] still, stop, restore, instep, after, actor
[ɾ] putting, pudding, metal, medal, hit Ann, setup, hurtle, hurdle
[t̪], [d̪] eighth, width, at three, you’d think
[t̠], [d̠] try, dry, entry, undress
[t͜ʔ], [ʔ] sit, out, button, sits, hint, can’t, commitment
[d̥] red, laid, headphones, birthday, watchdog