"That may be from the cold cold air intake and the MAT reading cooler air.
The truck is running cooler but that may just be from the weather"
In that case I think you found the cause of the low idle, a bad MAT or a problem with the intake manifold temperature where the MAT mounts (an exhaust leak blowing on it there? But that is a real stretch though).
The MAT needs to react fast to air flow rate changes, and any dirt or oil or soil on it will make it slow to respond. But at idle the air flow rate should be pretty steady, so ..... That leaves an MAT that is giving the ECM bad temp data (Called bias error), which you just solved by moving the MAT to a cold spot and lying to the ECM about the true intake manifold air temp.
In other words the MAT or the MAT wiring is telling the ECM the temp is 250 (estimate) when in fact it is 150 F (estimate). You fixed the bad MAT error bias for now by moving the MAT location (in part) I think. yes I know it is a different MAT.
Mine was a high idle problem caused by a bad MAT, it was doing the opposite of yours, telling the ECM it was cold when it was hot I guess. The way to test one I think is to use ice/water to test for 0 F, and boiling water to test for 212 F (at sea level) with an ohm meter.