My concern wouldn't be that the gas was old, as diluting it like you
did would have pretty much taken care of that issue, but I'd be
worried about how much water might have been in the gas.  One big slug
of water could have damaged things internally.

Matt
99 V-10 Super Duty, Super Cab 4x4
==============================

Had that problem on a '79 Cutlass.  A friend said that it was sticking
lifters, and that I should change the oil but put one quart of transmission
fluid in it.  That solved the problem for about four years, after which
I added a quart of transmission fluid again.

But if the problem goes away after another tank of gas, I wouldn't worry
about it.

 Normally a "pinging" noise is associated with fuel that is incorrect
octane, although most modern engines have knock sensors which retard the
ignition timing if it detects the engine knocking, or pinging.
 The noise began when you put the bad gas in it, no?
 Lifter noises are usually described as a ticking noise.  
 Without actually hearing the noise it's impossible to say for sure,
but I wonder if it didn't raise hell with the injectors when you ran
that turpentine through it, since that's when the noise started.  And
now having pretty much good fuel in the tank again didn't make the
problem go away.
 If it is indeed pinging that can damage upper cylinder walls.
 I'd recommend taking it to a pro and have him diagnose it, because you
could indeed be damaging it by driving it.
 They probably won't even charge you anything to just listen to it, and
there might be a technical service bulletin circulated to the
dealerships addressing this if it's been reported to happen by other
owners of this model of vehicle.
 The vehicle's still fairly new.  

Do a compression test and a leakdown test on all cylinders,  test manifold
vacuum at idle and at several rpm levels throughout the motors normal range, at
start up and through normal op temp.what do you notice ?. if you dont notice
any radical differences between cylinders(compression and leakdown) or between
hot and cold vacuum readings(manifold at various rpm) then I wouldnt worry
about it. Of course a friend of mine had his vehicle vandalized , a dude poured
two liters of orange soda in his gas tank(admitted to it , volunteered info
after a severe severe beating)(in middle of really, and prior to a worse
session and a talk with the cops followed by his arrest) truck was a gmc with a
v6. Needed new injection header gizmo(looked like a spider, forget the specific
name) and due to bent valve stems  and a warped head, the dealer he wound up
going to replaced the entire motor to the tune of roughly 7 grand. Luckily the
police report and the guys coerced admission /arrest onvinced his insurance
company to cover damages and cost of repairs minus his $500 deductable. Look
out for watery sh.t in fuel, it does not compress well when it is in sufficient
quantities and it will destroy the hell outa a motor. Larry got lucky as hell.
Hopefully , you  are even luckier.
Cheers,
MLM