Dont worry about that gauge just yet.
Have you turned the pump up yet?
My pyro is in the elbow directly before the turbo and until I bumped up my pump timing my gauge was reading really low just like yours.
I bought a new gauge and saw the same temps so dont waste your money on a gauge just yet.
Turn up the pump a bit and see how the pyro changes with it.
You will see more boost with more pump timing also. :Sly You will feel the extra power in the seat after your pump is adjusted more. I had to bump it 2 times. I first adjusted my pump to banks suggestions and then went back in and bumped it again because I had more room to grow.
I am seeing up to 850 degrees when pulling a trailer up a hill now and when I am accellerating onto the highway up the ramp full tilt I see the pyro jump up to 500-650 degrees.
Turn it up
Eric