Don't get concerned about the high pressure right after startup - I get that too and it caused me some confusion at first. The pressure drops over the first few minutes - should end up down around 20 to 30 PSI at idle. I used teflon tape, but I first made sure that the threads were cutting through the teflon. If you're really worried that you don't have a good ground then use an ohmeter to check between the engine block and the ground connection on the case of the sender. By the way, I'm not monitoring the pressure directly - I put some electronics together to alert me via a sound alarm to a drop in oil pressure in corners, so no "gauge" per se, just a threshold detector.
Eric
