Rover lost alot of 03 engines due to bad oil pumps. At the pressure you are talking about, I wouldn't drive the truck till; you verify the pressure both at an idle and 2000 RPM's when cold and at operating temp.
If still low do an oil pump replacement before it is drive much more or you'll be looking for an engine.

 

I forgot to mention he did also replace the sender unit which seemed not to do anything. Any clue on how much I should be paying to have the oil pump replaced? It would be helpful to have a ball park so I am not taken to the cleaners.

 

Mid 20 pound range at idle going up to mid 40's at 2000 RPM's.

 

I had this exact same experience with my 2000 Grand Cherokee: Ran the pressure tests, replaced the sender unit, replaced the oil pump and ended up having to replace the engine...all told: $5,000.

The oil pump was indeed the problem, but by the time it was replaced the damage was already done...crank bearings had worn to the point that even a new oil pump couldn't maintain the required pressure at idle, so the oil light would come on. I had unwittingly inherited this problem from the previous privateowner just one week after I bought it.

Moral of the story is: If the oil light is coming on at idle, don't wait to replace your oil pump. Stop driving it, get it towed and replace the pump.

Since I also have an '03 I'm considering changing my oil pump for the new improved design even though I don't have the oil light at idle...yet!