Both my tub and sink drain very slowly upstairs. They each have their own pipe that runs to the vertical drop. I'm wondering if maybe they are not vented properly, or something else. The pipe running to the verical drop is galvanized pipe. The sink is about 1 ft from the veritcal drop, and the tub is about 3-4 feet.

"both my tub and sink drain very slowly upstairs."
Do you hear a gurgle when you drain anything? You may have to have the lavatory vent snaked out to be sure it's not the vent. If that's not it then both the lav and the tub drain needs to be snaked out. Good luck, Tom

"Do you hear a gurgle when you drain anything?"

I don't hear any gurgling. If just a little water is running, its fine, but as soon as the water covers the hole, it starts backing up, and you get a foot bath with your shower... similarly with the sink.

Snake the lavatory roof vent. Put out enough cable to get to the base of the vent and about 15 feet more. If that don't get it then snake out each branch by itself. Good luck, Tom