I need to save the cash right now for other things, so I just ordered a glowshift (cheapo, but made in the same place as prosport, as I understand it). If it reads differently, at least I will know it was the gauge or sending unit at fault. I'll get some nicer gauges when I have more cash available, or when I do my VE+T swap as accurate oil pressure readings will be a lot more necessary.
I'm also going to run new wire from the sending unit to the gauge itself, just in case... and a fresh ground to the manifold.