Jer, don't go to the bother of swapping it out yet. Just plug it into your other motor or another probe laying beside it on the bench. The 600R's ECU needs to see a probe in order to get an EGT reading, but since you're not actually starting it the EGT reading is of little importance... Don't try to actually start it on the bench, just initiate a start sequence with no propane and see if the motor pulses as it should in a normal start up. When you see it do the usual cyclic RPM routing, you've got the problem licked and it would then be worth changing the probe...

Kelly