The expression "tortoise pace" usually refers to something moving slowly or at a leisurely pace. If you're looking for synonyms for this phrase, you might consider using "snail's pace," "slow-crawling," or "tardy." If you want to convey a sense of slowness while also emphasizing that something is steady, you could use "plodding," "methodical," or "deliberate." Alternatively, if you want to describe something that is progressing at a steady but slow rate, you could use "gradual," "protracted," or "incremental." Regardless of the particular synonym you choose, any of these expressions can help you describe something that is moving along slowly and steadily.