You had mentioned having some of the fittings, etc so I figured you might have a valve in with the mix....that"s what I get for assuming... You could do a test where you tee in and do what your talking about and just stall the auger and see what the pressure but it"s not going to be a real indication of what/where the problem really is. By that I mean if the problem is internal to the auger and it"s bypassing pressure when it stalls, instead of letting it build enough to turn, then your going to show a low pressure in the system regardless of whether the machine is the problem or not. By the same token if the problem is with the machine then your also going to see a low pressure when the auger stalls.
Basically the only sure way to test the system is to eleminate even the possibility that the auger is the problem because when it"s attached to the machine the test results are going to be basically the same (low pressure) regardless of whether the problem is actually with the machine or something internal with the auger. That"s the best way I know of to explain it, I hope it makes sense.