He said the radiator and water pump and thermostat was already replaced.
Although it's possible there was a faulty replacement for any/all of those parts it's a little unlikely.

So to compress everything down...
-Burp the system
-Test/Check Fan Clutch
-Replace Rad. Cap (should've bought a new one when rad was replaced)
-Check lower rad hose to see if it collapses (and that it isn't HOT)
-Make sure coolant has correct ratio
-Check for blown head gasket <--probably the least likely one

 

I'm betting burp!

 

So i ran it on a hill and it started to run like crap, the upper rad hose is cold.. lower is hot

 

It took about 15 to 20 minutes running to get the air out of mine.

What made it run like crap?

 

Whoa! It should be the opposite. You stated the water pump was new. Sounds like you have the wrong water-pump installed and it's running backwards (opposite flow of what these trucks flow).

 

Or if he somehow has the belt installed incorrectly it could possibly be making the WP pulley go in opposite direction...?

 

Good catch. Yes, check the belt routing as well, and be sure to drink your Ovaltine.

http://www.youtube.com/watch?v=zdA__2tKoIU

 

Never thought about belt routing, but that is definitely one explanation for the symptoms.

+1 on double checking that!

 

did you guys realize it was 2 different posters, with the same problem? this guy that parked on the hill never told us what his problem was.....

 

Crap. I missed that....Maybe the belt is on the wrong truck!