Why run a 160 thermostat..the normal recommened is a 180 and ex factory either a 180 or 195.
There is more than enough room to move air thru the radiator at speeds over 30 /40 mphs..If it is heating up then either there are blocked cores in the radiator ineffect reducing the size of the radiator, the radiator is incorrect application or the bottom hose reenforcing spring has corroded and dis intergated sucks partly closed at rpm....and the bits block the cores
Once I am off the highway the temp will start dropping back down and actually work its way down to about 175 within 5-10 minutes of idling
5 to 10 mins at idle is one hell of a long time...a good radiator will drop highway temps withing 1/2 to 1 min max......and at idle u far less air passing that u would at a higher speed..which indicates the above or you have something serious wrong in the engine its self..like timimg way the hell off or mixtures way the hell out on the cruise circuits..or both.
I believe u are chassing up the wrong tree here....
Test your theory, remove the shroud and head out on the highway...the ultimate open flaps right?
The radiator swap is because the stock 1 is leaking at the weld for the drain plug threads.
So I gather u dis not have an issue before and now u do...And replace a raditor because of a leak around the drain plug...thats crazy...a minor and inexpensive fix.
If u didnt have an issue before and now do , with the same air flow, but a radiator that is meant
to have better cooling properties .....doesnt add up.