gpu rx 6800xt

Hi there I have Rx6800xt and it's ok when I run benchmarks like furmark or heaven or OCCT and .... But when I play game ( any game but start in Forza 5 ) and run it ( don't matter what setting I play 1080p low or 1440 p max ) PC restarting and some time SAM (resizeable bar) disable in windows...