Will I have issues getting a tourist stamp on my new passport without a letter from the embassy in Thailand?

An American expat who recently received a new passport without an accompanying letter from the American embassy in Bangkok is seeking advice on whether this will affect his ability to obtain a tourist stamp in Thailand. Most commenters indicate that it is no longer necessary to have a letter from the embassy, and suggest bringing both the old and new passports to the immigration office. They clarify that tourist visas cannot be transferred between passports but that individuals can carry both passports while traveling.