Well to take up the question: "How long has the reformed church grappled with the election & predestination? " Answer: How long has the reformed Church existed?
The problem as I see it is in way we apply the words election, foreknew and predestined.
It seems that the majority meaning or intent of the word election is simply choice and refers to choices, not so much of people, but of attitude or purpose. Consider Rom 9:11
(for the children not yet being born, nor having done any good or evil, that the purpose of God according to election might stand, not of works but of Him who calls)
it is clear that the 'purpose of God' is the object of 'election' not the children. They are the beneficiaries, not the elected ones. again in Rom 11:5
Even so then, at this present time there is a remnant according to the election of grace.
Here again, it is 'grace' that is subject to election, not those who benefit by that grace. looking further, Rom 11:27-28:
For this is My covenant with them,
When I take away their sins.”
28Concerning the gospel they are enemies for your sake, but concerning the election they are beloved for the sake of the fathers.
The Covenant is the thing elected, not the people.
1Thes 1:4 refers to the election of people, so in a looser sense does 2Pet 1:10 The point about election of people is: we have to throw our hats in the ring to get a vote.
It seems to me therefore that to use 'election' in the context of preordination or predestination or even foreknowledge is to ignore the plain truth of the texts.
Now Predestine is a bit of as shocker! It does not mean to set the future course of events; as in 'set in stone'. That gives an entirely warped view of God's nature and purpose. When God 'Predestines' someone or something, He goes before....prepares the way...guides the voyage as it were, see it through.
Might leave 'foreknew' for future discussion

God Bless,
Kevin