Double check to make sure that the front gas tube entry passage is aligned with the passage in the gas block (you don't have the gas tube installed upside down, or the block roll pin in front of the tube cross passage for it), and the tube to block/ block to barrel is leaking badly.
On the tube to block passage, just pull the rear set screw with the block off the barrel and you can look straight up the set screw channel. If needed and the gas tube side entry is not perfect with the block passage, you can use a drill bit to enlarge the side gas tube entry channel (don't go buck wild and screw up the set screw threads in the block).
In regards to leaks and how to check for such, CLP around the tube to block and block to barrel front/back seams, then use a tube on the end of the gas tube in the upper receiver to pressurize the gas tube to around 100lb of air. Also to note here, when the gas block is set, you should be using Loctite on the set screws to make sure they are not backing out. If the gas block needs to be pulled later, donor allen wrench in the set screws, glow the donor wrench with a blow torch to transfer heat to the set screw to break the loctite bond (will smell a sweet smell when the loctite breaks down), the switch over to a new allen wrench to back the set screws out.
Lastly, make sure that the gas tube is correctly aligned with the carrier key. To check this, pull the bolt off the carrier, and with just the carrier and key, dry fit them into the upper receiver. The gas tube enters the key when the carrier is about 1' from touching the front of the barrel extension pin, and should be able to feel if they are aligned correctly.