2005 L59 Used or Remanufactured?
 

I bought this truck knowing it had low oil pressure at idle when cold. I am trying to decide how to fix it. Should I replace the oil pump or swap out the engine? I am leaning toward the swap, but I need some feedback on where to buy a good engine. Any opinions? This is a work truck in fair condition. Does anyone know a really realiable builder?

You might want to have someone actually measure the oil pressure to make sure it's not the gauge. You say it's only low at idle when cold, it's OK when warm and at higher RPMs? A rule of thumb I've always herad is 10 PSI per 1000 RPM. With that said my 04 GMC read 30+at idle and 40+ above idle.