I recently purchased a 1997 GMC Sierra XC w/5.0l that wasn't running. After tinkering with it for a month I got it to run and drove it for about two weeks. I managed to replace the radiator, updated the spider fuel injectors, changed all of the fluids and filters. After that second week I was going down the interstate and noticed my oil pressure dropped to 20psi and the engine was knocking hard.
Regards,
Jose