How's it going,

So I recently bought a 1990 2.9l 4x4 Ranger xlt used. When I test drove it everything was working like a dream. Picked it up and started driving it home and halfway home the oil pressure dropped to nothing, when I give it gas and take the rpms to about 2500 the oil pressure goes back to normal and then drops as soon as my foot is off the gas. It has started to stall out on me when I throw it in reverse as well. Took it in for an oil change yesterday and they said that the oil pressure sensor is covered in oil, would this be causing me the issues that I am having? Just trying to get it running decent again so I can get around town. Any advice would be greatly appreciated.

Thanks.