I have no clue why its starting to feel like this but when I had my timeing adjusted to +1 over stock timeing to get more hp and tq. My car will hit full boost at 5k then it feels like it wont pull any harder after 5k. My timeing was at 18degrees.

 

You have an LS engine. Dont be surprised at all, it makes perfect sense.

 

Befor when the turbo was first put on it was pulling all the way through the powerband now it feels like I lose all my tq after 5k.

 

did u check your plugs? what are they gapped at?

 

Im not sure there NGK's like the oem one's NGK 11's.

 

you could be misfiring up top and losing a shitload of power. Try getting some 1 step colder ngk's and gapping them around .028-.030