Welcome to the forum D.
Drop the pan and have a look at what lies within. Then take it from there.
When letting out of the throttle, the torque convertor unlocks and puts it into a sort of a coast mode.
It could possibly be the TC clutches is getting bad.
Another possibility that comes to mind...
Welcome to the forum Lars.
First item, or next item to do an uprated component on is the harmonic balancer.
If You can not afford a fluiddampener then go for a new GM Original.
The belt drive pulley is also a suspect item.
Either of those gets out of whack and it can bust crankshafts, and or...
And a happy fathers day to You guys too.
And the clan of the entire truck stop.
And now I ask, @Paveltolz whats that emblem on front fender of Your truck ?
The body shop has the doors done.
Their person thats a front end specialist has not had a chance to look over the front end for what caused the steering to get tough then pop and free up again.
My guess it is the drag link.
Just avoid the parts stores Dex 6 fluid.
IDK about the amsoil regular transmixer fluid, if its all the 6 variety, or, if they too have two different grades of Dexron.
Yeah so what @ak diesel driver said, either rebuild Your transmission yourself or have a very, very, reliable shop rebuild Yours.
Be very careful the shop You choose.
Some shops are very warm on warranty work, even after enough times to make the transmission right, to shops that are effe you on...
/\_/\_/\_ WHAT HE SAID _/\_/\_/\
Do a search in this forum about the transmissions, or go to the transmissions portion and start reading.
Just since I have been a member of this forum, there are enumerable threads about people that made the purchase of a reman transmission from some parts...