"4 slabs at 2.5lbs each"
Do you mean 4 individual cut ribs, or 4 racks?
Racks of Plates are typically 3 bones, sometimes 2 bones.
3 bone racks average 5-7lbs.
Plate's bones are flat in cross section.
So I'm curious what you have.
I prefer to cook mine at 275°-300°, with no wrap.
They are usually tender and well rendered at 205° -210°.
A full rack typically takes approximately 5.5 - 7 hours.
Beef Chuck ribs are a little different.
Description says beef plate short ribs.