Pedal vibration only happens when truck is warm/normal temp

So I know there’s an infinite amount on the pedal vibration in the third gens and I’ve spent tons of time reading them all but mine seems to be different, the vibration comes at around 40km/h and up with light to moderate acceleration and isn’t present when you step on the gas, when I put it in 4x4 it doesn’t completely go away?? So I think I can rule out the bad needle bearing but the weird thing is that it won’t vibrate when the truck is cold/ not quite at regular temps, what does this mean! Is it bad diff fluid or trans fluid? I don’t understand why the colder temps prevent the vibration and I’m not convinced the ecgs fix is necessary because the vibration should COMPLETELY go away in 4x4 correct?
Thanks a lot