I am just wondering if there is anything else besides gravity or velocity that causes time dilation in regards to special relativity or other theoretical models of our universe.
From a non-relativistic viewpoint, it seems as if we assume that there is no time-dilation (essentially assuming absolute simultaneity) unless there is some effect, like velocity or gravity.
However, from the modern relativistic point of view, time-dilation is the default situation because the essence of time-dilation is that there is no master clock that ticks for the universe. There is no absolute simultaneity. Instead, along each observer's worldline, that observer carries her own clock (or better: wristwatch)... and generally, the time difference between two distinct events is not universally assigned. (There is no such thing as "THE time difference"... but rather the time-differences assigned by various observers.)