Oil pressure sender?
 

So I had my tranny put in at the dealership(I know i shouldnt but) and after that my oil pressure gauge quit working. I think it has to do with the little black box below the slave cylinder. What is that? So I bought a AEM oil pressure gauge with a new sender. The problem is the stock one has more of a taper to the threads than the Aem and it wont screw in. They are the same size just the stock one taper's more. What should I do to get it to fit? Thanks

It's a condenser which conditions the signal to the OP gauge.
The gauge will work without it, so that's not your problem.

So what would it be? Here is what happened. The oil pressure gauge worked fine until i had my tranny put in. I towed it down to have it put in and towed it home. I started it to take it off the trailer and it spiked out as high as it could go. I let it warm up and it dropped to nothing and never worked again. I just took it out the other day to try to put the AEM one in and ever since I put it back in it has been slowly rising. It doesnt move with the Rpm and doesnt drop to 0 anymore when i shut it off. When I say slowly I mean it took probly 2-3hours of driving to get it to 30psi and thats where it is at. I would like to get the AEM installed but the threads arent as tapered. Any help would be much appreciated. Thanks

If the OP guage pegged out I'd guess it was shorted out.