I looked in the Modesto Bee obituaries from 02 September to 13 September 1989. I looked at the front page and the front of the "Metro" section for the 2nd, 3rd and 4th, too, figuring anyone who died at age 30 might have been in a car crash. I didn't find him.
I checked the city directory for 1985, 1987 and 1989; no Mifflins at all. I checked the 1989 phone book, again came up blank.
I called Lakewood, the largest cemetery in the county, and Franklin & Downs, the biggest funeral home in the county. Neither one had him.
The county used to let us look at death certificates; now, out of fear of identity theft, you have to be related to look at them.
There are no Mifflins in the current phone book either.
I apologize for raising your hopes over on the Mifflin surname page. In my experience, if someone has an obit, your chances for a copy are better on a county page than on a surname page, but there are no guarantees.