So my mains a warrior and I decided to pl a shaman into the 80s and all my slows are pbae whats up with that? Do I just use an older slow or an AA slow or just the pbae slow?
You've managed to go back and find your best Haste at lvl 64. You need to go back further in the spell book, your best Slow prior to 83 is the lvl 51 Turgur's Insects. You could also use Langor (Lassi) line as well. There is an AA version of Turgur's Insects as well.
There isn't a new single target slow every five levels, because there would be no point. They have no intention of giving players higher than 75% slow, which is what is on Turgur's, Balance of Discord, and the Counterbias line. Counterbias keeps getting upgrades, not because of the slow, but because of the heal portion. Likewise, the Drowse PBAE line keeps getting upgrades, not for the slow, but for the recourse portion.
As others have said the slow has remained the same for a very long time and after you get the AA Turgur's swarm you can use that unless you need to slow many at once with the ae slow.