Overheating
 

I just put a junkyard 360 into my 1997 Dodge Ram, I put water in it and all that, but its still overheating, and I ran it with the cap off, trying to burp it. It only overheats while just sitting at idle, which is at about 5-600. Any suggestions? Also at idle it sounds like it might be going from like 550 RPM - 600 RPM and comes back down repeatedly, how could I make it just sit steady at 600? It just sounds like its going up and down every five or ten seconds, weird, not too bad, but slightly annoying.

So in short:
1. What would cause my truck to overheat at idle with enough water in the radiator?
2. How can I even my idle out at a flat 600 instead of it waving from 550-600 constantly?

Check your fan clutch for the overheating. If its bad, it a good idea to change the water pump with it.....unless you just put a new one on.

I used the one from my old motor, which worked fine, but the only reason I used it is because I didn't wanna take the fan off and put it on the new motor, which came without one. So I just swapped the whole thing.

Have a look around for vacuum leaks. That is generally the cause of unstable idle.

I know for sure that 75% of my vacuum lines are f'd. Do you know where I could buy all the vacuum wires online already connected and exactly what I need or is it more of a "Buy a ton of vacuum lines and rig it" kinda thing?

The latter. :) Buy several feet of lines, and go for it. :D

Did you install a new water pump and new quality thermostat on that junkyard motor? Its not uncommon for the water pump to have the fins worn off of it and thereby lack the ability to move water through the block. Also, another thing I do is to pull the freeze plugs and dig all of the crud from around each cylinder (plus flush each area the freeze plug was removed with a water hose) and re-install new freeze plugs.

It was not a new water pump, it was used, although I did put in a new thermostat. I plan on rebuilding/building my old engine, so I will definitely clean out those freeze plugs when I do that. Thank you.

The truck stays around 180-190 while driving but if it's sitting for more than 5 minutes it'll go past 200 so I'm not too concerned about it, I shouldn't be letting it idle that long anyway I think.

Alright so no matter what if I'm driving or not it will slowly creep past 200 to about 210-215 then drop back down to 195-200 when I start driving again or have the Heat cranked. It can and will go past 215 if I don't start driving again as well.

What is causing this? It has coolant and the water pump/thermo is good.

Might want to swap out that thermostat. Ensure that you install a high quality thermostat, like a Stant Superstat. Cheaper thermostats are common for having high defect rates.

Also, are you sure you got all of the air out of the cooling system?