Finally A Run With Nitrous But Inconsistent? Whats Wrong With These Times???

You should ask that mechanic if he used teflon paste or tape. If he knows what he's doing, then he should have known that you should not use the tape. It can clog up your solenoids. You should check out your nitrous filter (before the first solenoid). Unscrew it with a wrench and check to see if there is any debri in there and clean it out. You may want to unhook the nitrous line from the bottle & the tank and blow compressed air through it to make sure there is no blockage.
Is this the kit#5115? If so, you have a fuel pressure safety switch that is hooked up to your fuel line (where the Schreider valve is on the passenger side of the engine compartment). This switch detects if your fuel system is not supplying enough fuel "volume" to make the adequate boost in fuel pressure. If at any time during a nitrous run, your fuel pressure drops below 85-80psi., this safety switch will not allow the nitrous to go into your motor. It's a great safety feature which should never be bypassed. If your stock pump is still in your tank, than that is most likely your problem. You should upgrade to at least a 155lph intank pump, if not a 190lph intank pump. That should be sufficient for nitrous shots up to around 100hp. If you ever want more juice than that (like me!) you would have to install an additional external inline pump to boost the volume of fuel even more to mix with the additional nitrous.
You really don't need to purge the system. Let alone, after every run. The little bit of air that is in the 14-20 inches of the braided nitrous line, between the NOS solenoids and the throttle body is the only place that "regular" air can collect. I doubt you will feel a difference between a non-purged run and a purged run. But that doesn't mean don't get one. I just don't think that is your problem. Although purge valves do look cool as hell! I'll be getting one eventually, but not so much for the performance gains. LOL. Let us know the outcome.