Allright, a little update of my truck.
Got it running perfect today!!! I first did a compression test this morning and found out that i had zero compression on cylinder number 8... that can only mean one thing: problems somewhere on top of the engine. So i took off the valve cover to check the valve stems, springs and rockers and while i was taking of the cover i felt something loose under it.
I'm almost ashamed to tell you guys how a dumb mistake I've made

I forgot to tighten the rockers of cylinder number 8....

So I've torqued the rockers and checked the others too (well, i was doubting myself for all of the other repairs too now...), started the truck and did a test drive.
Man, this is pure power now! Left two nice black rubber stripes behind when i took off

SO problems solved after 2800$ worth of parts (300$ more than i should have bought) and sleepless nights wondering what else could be wrong... learned this one the hard way.

I would like to thank all of the people who helped me on this topic, i really appreciate this!

Greetz,

Bigster