Where is the oil sending unit on a 98 silverado with 350 engine?

The oil pressure sending unit on a 1998 Silverado with a 350 engine is located on the driver's side (left side) of the engine block, near the front. It's a relatively small unit with one or two wires connected to it. You'll likely need to look closely and possibly use a flashlight to spot it. It's usually near the oil filter but not directly on top of it.