You will get two schools of thought with tire pressure!
There is the group the believes that the yellow sticker is the do all for all loads. For most this is about 80 psi.
Then there is the group that use the yellow sticker as a guide for loaded, adjust for the unloaded condition. Running lower rear pressure when unloaded based on weight, this will improve traction and tire wear.
I am with the second group, instead of adding weight to the bed to reduce tire spin, lower tire pressure to get a better contact patch.