Ford Super Duty (1999-2016) :: Trans Howls In 4WD High

first heard it a few weeks ago after the wind storm hit us here in nj, my girlfriends grandmother has her fifty foot pine tree rip out of the ground in her front yard. since it was only thirty feet from the street. I said hell ill drag this sucker to the road and cut it up there instead of dragging everything by hand. I figured 4wd high was good (don't know how heavy a pine tree this sized weighs) and I hooked the tow strap to the tree trunk and started to pull. first 4wd high was struggling but the real problem was this high pitch howling i was hearing, went about ten feet and the noise started to bother me, so I stopped and put the truck in 4low the noise stopped and the truck drug the tree with zero effort.

So I didn't think much more of it till today, got a little dirty trying to take the dog swimming and needed 4wd, as soon as i started to hit the skinny pedal and the motor made the tires turn that dam howl came back! rocked the truck a few times and ever time the motor lugged from trying to spin all three tire the same howl came back. switched to 4low to get out and the noise went away?????? Went back to 4high and sure enough the howl was back? regardless i got out but now i have this howl when using 4high and I am really working the truck hard in 4high. I am thinking torque converter is slipping making the sound and4low multiplies the power enough to make it go away from the ease it now has to spin the tires? I am gonna go tomorrow and climb a few hills and see if i can get the howl to start again in 4high...