It will only have as much pressure as is allowed by the radiator cap. The system has a pressure release so it doesn't get over-pressurized, usually around 20psi.

 

I think you probably have lifted the head.Is there any dried coolant on the block right below the heads? Once they cool off they might seal up but can do it again.

I never pressurized my cooling system but I noticed I had a small coolant leak between the head and the block after the truck sat a few days.I stretched the stock TTY head bolts. I took everyone's advice and put ARP studs and LS9 gaskets in it.I was running 14# of boost and 20* of timing.I backed the timing down to 18* since then.

Also have you checked your oil to see if coolant was pushed it the crankcase?

 

You lifted the head enough to push coolant. My stock 4.8 did that on an aggressive 14psi e85 tune. After that I couldn't run over 10 psi of boost with out it pushing coolant out the over flow tube. 8psi it was fine, but turn it up a little and would push coolant out of the over flow every time. Time for some heads studs and new gaskets.

 

well crawled under the truck to check out the seals under the heads and couldnt find any evidence of a blowout, no tears running down the block or stains on the block or any thing so i decided to pulley down from a 3.7 to a 3.4 to see if it was a gasket cause this would for sure take it out . so i go take a rip down the street and around the corner and dam this thing pulls hard now in the mid range but i think it might be slipping up top but anyway i popped the hood when i got home to see if it puked any more coolant and it didnt although the radiator hose felt pressurized again (maybe thats normal??) i got a new thermostat on the way so ill see if that makes a difference or not.

 

My coolant reservoir wasn't sealed all the way around, and when it was hot outside, it would act like it had all the pressure in the world pushing on it. Coolant would **** out of the side and my truck would start to overheat. Once I replaced it, the truck never got hot and no leaks.

 

Block test is way easier(and cheap), and quicker for finding out if you have exhaust gasses in your cooling system, compared to a leakdown test. Here's a couple vids I found on youtube that explain the test. The first guy kind of goes off on a tangent in the second half of the video... lol

Testing for leaky head gasket - YouTube

How to tell if your head gasket is blown - YouTube

 

thanks for the videos i will give it a try . another thing truck isnt over heating at all held right at normal at 205-210 as always.

 

Probably lifted. Smart thing to do is fix it before it goes boom 1/2 BBC studs and new gaskets make sure everything is still flat.