do voiceless th sound in american accent persists for all

wa im sayin is that ive noticed on many american channels and many native speakers that where the voiceless sound of th as according to neutral accent is necessary they dont give that voiceless th everywhere for e.g. they say word something as sometin t like very flat without puff of air so is it true.

Secondly ive heard that the only thing that makes someone sound american is intonation and stress that americans do when speakin, ok im sayin that even if a person is not movin his physical components of speech in exact american way even then he may soundamerican by giving intonation and proper stress in his pronounciation.

Voiceless consonants are uncorrelated with a "puff of air." A voiced consonant is one that is pronounced with the vocal cords vibrating. In a voiceless consonant, the vocal cords do not vibrate.

English has two dental fricatives, one voiced, and one voiceless. The voiceless version of the two is much less common, and there are very few minimal pairs that place the two versions in contrast with each other (either and ether come to mind, although that depends on the pronunciation chosen for either). When in doubt, use the voiced version.

The distinctive sound of American English is due to distinctive ways of pronouncing certain vowels and consonants; intonation and stress are relatively unimportant, although they are different from some other pronunciations of English, in some cases. American intonation tends to be more flat than that of most varieties of British English; stress is mostly the same except for a handful of words.

My dialect does definitely have /T/ pronounced as [T], but I do in cases replace it with something that is similar to what I think you're describing, which is an affricate [tT], where it is first stopped, but then released like a fricative; however, this only shows up word-initially, and then it only relatively consistently shows up when a preceding word ends in /t/ (whether or not that is actually realized as [t], as it most likely will just be glottal-stopped, which does not prevent th is).

There are a few areas in the U.S. where -th- is occasionally pronounced like -d- , primarily New York and the rural South as in "What's a good-lookin' dame like you doin' in a joint like dis?" or in Chuck Berry's song "Gimme Dat Ding." To most Americans, however, it sounds at least uneducated, if not low class; New York street kids and gangsters are sometimes portrayed in movies as talking like that.