You did it right by plugging the PVC holes and checking for vacuum or pressure.
Usually you can tell with just you finger but a more accurate (and the factory test procedure)
is to plug one valve cover with a hose attached to a vacuum gauge. Any vacuum indicates a blown plenum but it sounds like yours is OK.

 

dodge 4x4, my truck is doing the EXACT same. My cousin is a mechanic and im going to school to become a mechanic and still cant find it. So far ive done, new plugs, new wires, new coil, new cap, new rotor, fuel system flush, flushed out injectors, sea-foamd entire system. whats funny tho now u guys talk about thermostats, mine never used to ping till after i changed my thermostat...... its not a 180 degree one tho....

 

i reamber like 7 weeks ago or so i dont no number 8 cynder burned its plug 2 times i mean i dont no wat that was about but that was the only week it happen i dont no if it has anything to do with the pinging maybe you guys knoe

 

and i guese the death flas is out im not doing that not going to loose all the power theres got to be way llike did these trucks do this when they were new? it seems llike it happens to alot of people

 

and the 180 term am i still going to have good heat in the winter with that and the timing chain whats a good kind to buy the one from factory

 

 

do these trucks ping from the factory

 

no. pinging is an indication that something is wrong in timing, fuel mix or octane, heat, or carbon buildup on the pistons (which holds heat).

 

ok so get this today is was doing it at all most idle i checked the the slake in the timming chain today and the plunm gaskit agin both fine

 

i dont get it im about to sell the thing and buya cummins