When an electronic sending unit is going bad, will it start showing lower readings, or just go out all at once. My fuel pressure readings are getting lower, and I'm trying to save some money to get a new pump, but wondering if it could just be the sending unit. It would make more sense to me for it to just quit, or start reading erratically, but I'm no electrical engineer.

 

Seldom do the senders fail like you describe your symptoms. This sounds like a lift pump is heading south.

If your fuel pressure is below 5 psi during the starting cycle, and below 10 psi at idle, replace the lift pump before you end up having to replace the VP44 right along with it.

 

I've seen the senders fail in all manners of ways. One of the most common is reading the highest pressure it usually sees and zero with nothing in-between.
Might be a good idea to hook up a mechanical gauge to verify what's going on. Any pressure gauge will do, you can pick up a water pressure gauge for under $10 at most hardware stores, maybe a couple of plumbing fittings and you're set to go.