With agonizing slowness can be substituted with synonymous phrases like "at a snail's pace," "with turtle-like speed," "inching along," or "creeping along." These phrases all describe movement or progress that is painfully slow and tedious. Other synonyms of "agonizing" include excruciating, unbearable, or torturous. Combining these words with different adverbs can create different variations of the phrase, such as "with excruciating slowness" or "creeping along at a torturous pace." These phrases are often used to convey a sense of frustration, impatience, or desperation in situations where time is of the essence.