What else could it be?

[chevychic]

My truck is progressively running worse each day.
It started out as pinging under load as I'm going up hills or passing someone. This is after the truck had sat for about a year.

So I did a tune up. New fuel filter, cap, rotor, plugs, plug wires. Adjusted float level, idle mix, rechecked and set distributor timing. Replaced all exhaust gaskets to eliminate exhaust leaks. Checked for vacuum leaks. Removed and cleaned EGR valve...getting ready to get a EGR blank out plate so I can get rid of it since all the other emissions stuff is gone. I've plugged the vac advance line and took it out for a drive to eliminate a bad pickup coil but I still had the pinging.

Through all the adjustments, I've checked the plugs a couple times and all look just fine.

After all this, I still have the pinging and now when idling at a light, it idles so low, if feels like it's going to die. But I've set my distributor timing and idle mix and all is set good so I have no idea what's going on. Vacuum advance appears to be working fine.
I've retarded the timing, advanced it, and all it does is affect how soon the engine starts to ping. It'll either start under medium load, or it will start under medium to heavy load. It's set to where it was running good before all this started.
Also, my gas mileage sucks right now. I'm spending $10 a day to get to work and back...I'm about ready to get my bike out.

When my car gets out of the shop so my truck can be parked for awhile, I'm going to remove the valve covers and see if anything looks like it's not moving right.

Next I'm ruling it down to carb, fuel pump or distributor. Distributor has less than maybe 2000 miles on it, carb was rebuilt 3 years ago so I would hope it would be less likely to be carb or distributor....but with my luck...who knows

In the meantime, am I missing something? What else could be going on?