Religion is the primary determinant and the tendency for religiosity among societal elites tends to wane over time, that includes the Middle Class suburbs. As religion has shifted more down market so too has the GOP.
Depends on where in the country. But they mostly run the gamut on social issues (i.e. abortion, religious liberty) but are left of center on cultural issues (i.e. immigration). That's why these voters reacted worse to culturally conservative Trump than they did to socially conservative Bush 43.
Also, contrary to popular belief, evangelical conservatism tends to find its base in the suburbs and among the middle and upper middle classes.
Suburbs were Republican for so long because of cultural issues. Busing and crime were the social issues par none that motivated lily white suburbia to turn out for people like Nixon and Reagan. The threat of "those people" moving in and causing crime was an omnipresent reality that motivated GOP voting habits.
The immigration issue played as a crime issue in a lot of these suburbs. Remember if you go back 12 years, the biggest border hawks and anti-pathway legislators, were those in the suburbs of SoCal (Duncan Hunter Sr, Elton Gallegly and Brian Bilbray), Texas (Lamar Smith, Tom Delay and others), Denver (Tom Tancredo), Charlotte (Sue Myrick), and Pheonix (JD Hayworth).
Pat McCrory and Mitt Romney, both found their bases in high end, high educated suburbs ran as business Republicans generally, but used immigration to get to the right of their primary opponents. McCrory ran adds in 2008 about cracking down on "Crime, Gangs and Illegal Aliens". Romney attacked McCain and Rudy for supporting amnesty in the Comprehensive Immigration Reform disaster of 2007. He used the issue again in 2012 against Rick Perry and Newt Gingrich.
This is not by accident either, the rising demographic, pushed the traditional power dynamic to the extreme since it feared losing power. You don't see it now as much, because that has come and gone and most of these districts are represented by Democrats now and maybe had a an immigration moderate serves as a transitional prelude to the rising Democratic majority. A historical parallel to the same dynamic is the UES side of New York which went from 1930s: Anti-New Deal Establishment Conservative> late 50's: Liberal Republican > late 60's: Liberal Democrat.
Call it the three stages of transitioning districts/states: Reaction to Rising Democratic>Moderation with Rising Demographic>Consumed by Rising Demographic
The UES/wealthy parts anyway is still very much establishment moderate Republicans.
