the last comp. test was done when it was installed. it was 2 1/2 years ago so i do not recall the exact comp. the truck has not used a drop of oil since it was installed and it does not smoke. it was so nice when i installed it that there was still hone marks on the cylinder walls.
You can do a compression test while the other 7 cylinders are running. This will actually tell you pretty fast which cylinder has bad valve train, and which side (exhaust or intake) the bad valve train is on.
A running compression test is different. It has nothing to do with the oil consumption/hone marks/rings. It is testing the breathing capability of the valve train while the engine is actually running.
Here is a bad video showing one being done while an engine is running.
They didn't cover all the steps like working the throttle under load, etc but nonetheless you can see the engine running with a gauge in it.
If you think you have a valve problem, and describe it as worse under load, it only makes sense to do that test. It's actually 3 tests. A normal compression test with all the plugs removed and throttle wide open, then a running test with 7 cylinders running at idle, then a very fast throttle blip. Those 3 numbers combined give you the whole valve train story. Normal test is for overall health and is the highest number. Running test number is much lower since engine is under vacuum and doesn't have as much air. Then the blip of the throttle momentarily fills up the cylinder. From there you can tell if you have a valve train problem on the exhaust or intake side. Not just a leak, but:
*pushrod/lifter/rocker issue that causes lash
*worn lobes etc