I have an slightly elevated t4 and occasional heart palpitations. tsh and t3 (liothyronine) are normal. what could this be? should i worry?

Probably nothing: Is that a total or free t4? A high total means nothing. On rare (very rare) occasions, people can have an abnormally high free t 4 and a normal TSH and have either secondary hyperthyroidism or central thyroid hormone resistance. But almost always if the TSH is normal the thyroid is fine.

Sounds like: Simple iodine deficiency since T4 has to be iodinated to formt3. There is a pill called iodoral, that is the modern equivalent of lugol's iodine.