Good to know that the rad was a straight swap, especially at such a bargain price.
Where did the foam sit, around the edges? If so, then they help force the air thru the grill and not to take the path of least resistance around it.
Do you have an OBD reader that you can use to get a reading of the coolant temperature? The gauges aren't known for being that accurate and I'm quite surprised that it shows any difference at all. So maybe the gauge is more accurate than most?