Depending on the size motor if it's a 4 cylinder 5 quarts of oil, 6 cylinder usually  between 5-6 quarts and a 8 cylinder 6 quarts.

If it has a 4.3 liter v-6 it should be a 3:55 or 3:73 gears or it could even been 4:10 gears

You could always call the always and give them the information and they could tell you who owns it.

If it had coil packs it best to change them out it may not be getting spark, and also check your plugs and wire you plugs could be fouled out and wires might be in bad conditon as well.

Yes you can put those on the vehicle will ride better you might notice alittle gas mileage difference but not much