I just got this truck not to long ago and I noticed that after it warms up and sits at idle the oil pressure seems to drop all the way down. Is this normal for these.

 

After your oil warms up and becomes thinner the pressure will naturally go down, but it shouldn't be that much. What does it read cold?

Check the connection on your sending unit. It could either not be grounding correctly or on its way out the door. Quick way to narrow it down is hook up an aftermarket gauge for a quick test to see what the oil pressure really is.

 

when cold it usually sites mid way between where it is now and that first line. when driving it stays up around the first line

 

My 85 is the same way. If it blows it blows but i had mine since july with no problems yet

 

Mine started to do that right before throwing a rod through the side of the block . You should have SEEN the kind of stuff in the bottom of my oil pan, i REALLY should have taken pictures of it. Probably 2 completely broken up timing chain guides, and enough bearing material to make 3 bearing halves. Not even powder, FLAKES. BIG ones. Anyways, i'd see if i could pull the pan and put some new bearings in and just check things out if it's not knocking. That oil pressure is for sure too low.