have a 2001 kia sephia , that runs good.

You can check you transmission fluid level at the dipstick. If it is full and redish colored, things are starting to look good for the trans. Also smell the fluid for a burnt smell if it is ok and you don't have any shifting problems we can rule out the transmission. also vacuum modulators are found mostly on older transmissions newer models are electronically controlled. It sounds to me like you have worn valve guides or seals, or oil blowing by the oil control rings. You need to do a compression test, or leak down test to verify this.