Strange behavior from RX580

[HristoBB]

Hey guys! Recently i bought an RX580 GPU and installed it in my Computer which has Asus 970 Pro Gaming Aura mobo and and FX8350 CPU clocked to 4.7Ghz. 
I have M.2 SSD and 2 Sata III SSD's .
But when i open GPU-Z my gpu only shows that it is running at 8x 2.0 PCI-E speeds.I do understand that AMD chipsets doesn't support PCI-E 3.0 but my old R9 280x was working at 16x 2.0 speeds and the Rx580 is working at only 8x. 
Not that my performance is bad i can play almost every game at maxed out settings at 1080p. 
Anyone knows what's the reason? 

[HristoBB]

Nope i'm not that stupid i already ran a couple of tests. Playing games running benchmarks stress tests,but nothing worked. It only shows 8x
And i have Sapphire Nitro+ 8GB with clock speed of 1411 and mem speed of 2000mhz,but i have overclocked it to 1440 and 2200 stable with no problems.
But it doesn't matter if it is clocked or not it only shows up as 8x 2.0