Slayer's solos are more of keeping the beat and time than taking care of the notes , and sometimes they just tremolo pick and move up and down the fretboard like in "Angel of Death".

As a general rule for playing fast solos , separate them into small licks , then learn each lick at a very slow tempo gradualy increasing speed and connecting licks together.
A metronome would also help.

"Seasons in the Abyss" , "Dead Skin Mask" & "Antichrist" are my fav Slayer solos ... Usualy , Slayer solos are short and easy to memorize & play.