I have a 2004 Silverado 6.0 I lost oil pressure one year ago and took it to a local mechanic he changed the oil ascending unit and the oil pump I installed a manual gauge so I know that it is not the cluster, the truck has about 20psi at 2200 rpm and 0psi at a idle I have been driving the truck for a year like this with no noise?

0 PSI at idle and 20 at 2200 is a problem. First I would check the general health of the engine. What kind of compression does it make? Is your oil pressure readings true? On a 2004 you can read the pressure straight off the computer ALDL under the dash with a diagnostic reader and it will give you a number read out instead of a a pointer on the factory cluster. You may want to confirm the factory oil pressure sender and manual gauge read the same. How is the new gauged plumbed into the oil system? If it is tee'd off the factory sensor there is a possibility there is a restriction in the setup causing one or both gauges to read low? If it turns out your gauge readings are accurate I would plan to have new rod and main bearings put in. However the cost to do so is probably more than getting a replacement engine from a junkyard. Used 6.0 are everywhere. Check ebay for "LQ4" car-parts.com can search your local junk yards as well. So decide if you want to put new bearings or a newer engine in it. If you decide bearings I would do it sooner rather than later as additional wear may damage the rods and crank. If you decide newer engine, I would save up the cash and just run the current engine until it dies.

I forgot to mention I bought the truck new it has 120,000 miles on it, it also has had regular service, the manual gauge has a cooper line going straight into the block were the oil ascending unit was located, will the computer ALDL read the oil pressure with the oil ascending unit unhooked, does it get its reading elsewhere? Thank You