99 Dodge Dakota Cooling System Problem

I have a 99 Dodge Dakota Sport Reg Cab, Short box, V6, 3.9L with 184 000km on it. My my truck overheated when the outside temperature was -38C. I was told that my coolant must have been low so what I did was fill it with new coolant and water mix. Now that it is running well again, I find that my temperature gauge is running a little high. My needle hits the 1 of the 100 mark on the gauge. If I recall right, before the overheat, my gauge needle would only go about a quarter way from 50 to 100. I got a coolant pressure pump from work and will try testing it that way. I also noticed that sometimes, l have a yellowish, green spot in the snow under my truck. Anyone have any suggestions on what my problem can be?

No money and trying to fix it myself.
Thanks