If you remove the oil filler cap does it release the vacuum ? If it doesnt then the problem is in the lower end. The pressure your getting is not a bad thing since it shows good seal on the rings. Hense the squealing noise is the air is being forced out where it isnt suppose to.
Since you put the engine in how long have you let it run and have you driven the truck around ? Almost sounds like the crank case vents are plugged. Was this block hot tanked ?
