Installing temp guage sensor(aftermarket)

Ok, I'll try to say this without writing a book. 2yrs ago when I bought the car both gauges worked intermittently but I thought the temp was reading low, not even registering hardly. Then, after killing the motor the temp gauge would slowly begin to rise almost to halfway mark. Bought the trio gauges and finally went the pipe fitting route, but was never satisfied with the results. The new gauge starts at 130 degrees and just like the old one, when I'm driving, it doesn't register at all. I kill it and come back 15 minutes later and it's reading 170-190.
So, last weekend (2yrs later) I decided since the new gauge reads like the old, why not get a new orig sensor and just try to fix the old gauge. But now the factory gauge is completely dead, I tried grounding the wire going to the sensor, but nothing. Shouldn't that peg the needle if it's working? My gas gauge is still working just like it always has. I would rather fix the factory gauge, but I've never even pulled the gauges out of the dash, and won't until I know what I'm looking for. Also, all this makes me wonder if my engine is even warming up to normal operating temp? The heater doesn't blow very hot.
And why is it heating up after I kill it? I understand that heat rises and the sensor is at the top of the motor, but I've never noticed one heat up that much after shutdown.
One other thing, when it sets and gets hot like that, it's hard to crank and the lifters clatter if I put any strain on the motor. It doesn't seem to run good hot.
Sorry, I'm no good at diagnosing. I'm one of them "tell me what's wrong and I'll do the labor" types. Thanks for all the input.