Oil pressure problem

I have a 1988 K1500 with the 4.3 V-6 and I have a oil pressure issue.
The oil pressure light comes on when it idles and will go out when you bring the idle up, so I don't know if the idle is too low or if there is not enough oil pressure. Just recently will driving on the highway after a bit the lifters will start to tap and it seems like it is not gettting oil to the lifters even at highway rpms even though the light does not come on at higher rpms, only when at a idle.
Has anyone had this problem or is the oil pump shot or what???
Any help would be appreciated.
Thanks

get a guage and verify the pressure. Sounds like your engine is tired and needs a little TLC

when its idling, take your oil cover off of your valve pan and look inside to see if its pumping oil to the top end. if not, change your pump immediately or you'll pop her. likely would be already damaged if you driven it much w/o oil pumping to the top.

yep, definitaly sounds like your motor needs some love, or TLC anyway. Do like planedude said to do and get a gauge to verify what kind of pressure you are getting. At normal operating temprature, my 4.3L has approx 30 pounds of pressure and goes up to about 60 pounds when engine is under a load (or @ 2000 RPM in gear). However, this seems to be the norm for any type of motor (vehicle).

But hey guys, since we are on this subject, any suggestions as to why I've noticed my oil pressure decrease to 25 pounds @ idle (warmed up) and 55 pounds under engine load of 2000 RPM?? Noticed this slight decrease approx 3 months ago. But I am certain it used to be 30 to 60 pounds but don't really know what the cause (or reason) would be.

It is most likely the oil pump

How many miles on the engine?

The oil pump is not the source of the problem. There isnt much gray area with an oil pump, it works or it doesnt. Since you have adequate oil pressure off idle, enough to keep the light off anyway, the oil pump is fine.

Your problem is excessive bearing clearance. As soon as a car is driven off the showroom floor, rod and main bearings begin to wear out. How long they last depends on driving habits, maintainance, etc. Replacing the oil pump with a high volume unit is only a band-aid. The engine will need a rebuild sometime in the near future. There are a few things you can do to prolong the life of the engine.

First, if you havent already, check the oil level.

As planedude said, get an aftermarket oil pressure gauge.
5psi will get you down the road, but would scare the hell out of me. Anything less than 10psi indicates a well-worn engine.

Run thicker oil. In the winter use 10w-30 and 20w-50 for the summer.
Thicker oil = more oil pressure.