on the engine
It is right behind the distributor.
The oil sending unit is located on the back of the block, directly behind/below the distributor.
if its a full size pickup, with a v8, the fuel pressure regulator is in the tank, its part of the sending unit
where is oil sending unit located on a 366 gasoline engine on 1995 gmc topkick
It is to the right of the Distributor about 2 inches.
The oil pressure sending unit on a 2005 GMC Sierra
Yes
Yes.
Where is the oil pressure sending unit located on a 2004 4.8 L V8 GMC?
Simple answer is that it doesn't have one.
it could be the guage, but that is extremely rare. i had the same problem as you, i have a 97 gmc sierra (same as Chevy in case you didnt know). the sending unit in the fuel pump is where your problem is. this comes as a 1 peice drop-in pump and you HAVE to buy the whole pump not just the sending unit. There is a fair chance of it being a short between the sending unit and dash guage, but it is also slim.
Replace sending unit.