daeman
+1y
Sounds like either your alternator belt is slipping or the bearings are squealing when you turn your lights on due to the increased demand on the alternator.
Was your oil really dark before you changed it?, you may have spilt oil on your block or chassis when you changed your filter. Your water pump failing would leave a puddle of coolant not oil.
Look under your truck and try and see where its dripping, then follow it back up to its highest point, should lead you to the source of your mystery fluid.
Unfortunately without pics, your the only one who can see what's going on, so a bit of detective work on your part will be required.
Let us know what you find.