2003 SE 108K
I have ignored intermitant lifter noise for the last 10k miles. Only happens when warm and not constant.Oil pressure is good. Synthetic oil.
Thoughts.

 

Check your exhaust gasket between the manifold and the "Y" pipe. An exhaust leak there can sound like internal engine noise.

Do this for a test:

1. After warm put the rig in D and accelerate faster than you usually do leaving your drive way. You should here the "tapping"

2. Now put the rig in "N" and slowly rev the motor to about 3k rpms..

3. If you don't hear anything during # 2 then it is an exhaust leak.
4. If you hear something during # 2, it should get faster and or louder with higher rpms which means there is something internal making the noise.

Where do you live? Maybe a thicker oil will help if it's not the exhaust leak...

 

you might want to consider doing an engine flush ( a debateable topic here) . How often have you been changing the oil, what oil are you using ? It is possible that some of the components in your valvetrain are worn, but let's start with the cheap stuff first.

 

Or as a temporary fix use a thicker oil like a 5w-40, 15w-40, or 15w-50 (Rotella, Mobil 1 etc.)

 

Why have you let it go for 10K, just looking for a more expensive repair???????????
Are you sure it is internal and not exhaust, have you inspected the entire exhaust area down to the cat back?
If internal, then start with the oil pressure test and don't come back with it is OK which tells us you didn't have it checked. When stone cold, check at idle and at 2000 RPM's and at operating temp. at idle and at 2000 RPM's. Give us those 4 sets of numbers. If low, then pull the pan and check the pick up tube and the pull the oil pump if necessary.
If the pressure is good, pull you engine down past the valley pan, inspect each lifter for wear as well as the cam, then check each push rod for wear and length. Still nothing, then pull the rocker arms, dismantle and look for wear on the shaft and the arms.
Don't waste your time with different oils and filters.

 

Will have the mechanic do the pressure check and put in a thicker oil tomorrow.

 

You didn't read or understand a thing I said, did you?????
Why thicker oil? If you are going to have the pressure tested, call ahead of time and leave the truck over night so they can cold start it.