Another coolant leak…

Just finished refreshing my engine recently. New oil pan seal, rear main seal and all gaskets except for the passenger side head gasket. After finding and replacing a leak in the hard line that runs under the lower intake mainfold I thought I was done. At idle there are no leaks and the engine sounds almost quiet.

After running it through some more tests I decided to maintain about 4000 rpm for about five seconds, and suddenly a huge column of steam shot up from the engine and the driveway got soaked in coolant. I had someone hold the car at about 4000 rpm again while I watched for the leak, and god help me it looks like there is coolant coming out from the valve cover. At idle there is no evidence of a leak, though. I can't tell for sure because of all the steam but there is coolant pooling on top of the driver side exhaust manifold after these tests. I'm going to find a pressure tester to know for sure but I'm having doubts as to whether or not I can get the cooling system to leak the way it did with a handheld pressure tester. Haven't seen any white smoke or milky coolant yet but anything is possible. I'm hoping it's a loose throttle body coolant hose but they all seem tight, and I know there are no coolant lines besides the turbo below the valve cover… Any ideas?