92 4.0l

I have a 92 that seems to be on crack. For a while, the oil p indicator has been eratic, especially after highway travel. I've been asuming it's a bad sensor (not too uncommon). Last week it bottomed out, and the engine was running like crap. During the time it was bottmed, my voltage was running exteamely high (~17V). Any ideas about that? Also, anyone ever changed an oil pump on one of these? I've heard you can do it without lifting the engine. True? Any and all help appreciated.