Whining sound while turning in 4HI/4LO and Transmission overheat

[Kareem Karame]

Ok, so this is my first time posting here, and I'm really hoping to get some useful feedback as y'all are truck people like myself. I've owned my truck for the past year and a half, and only began noticing this issue after I serviced and changed all my oils (Transmission, and both diffs.) We're talking about a 2014 GMC Sierra 1500, 5.3l V8, SLT trim (if the trim matters).

 

Here's what happens. On 2HI it runs great, no sound, smooth as silk, and transmission temp hovers at around 91 Celsius (195 Fahrenheit), and when I use to shift it to 4HI or 4LO, it rises up to MAX. 105 Celsius (around 220 Fahrenheit), and still smooth on the turning. Once I changed all my oils, suddenly there is a LOUD whining sound coming from beneath once I turn (not even sharp turns), its really sluggish, and the transmission does not take long to reach temperatures of 120-125 celcius (245-260 fahrenheit). 

 

I've already rechecked all the oils, and everything is clean and at a good level, there are no leaks, and I've used oils as per the owners manual. Any idea what I'm looking at, or what I should be checking? I do not want to blow useless money on monkeys clanking around in my truck for no reason.