Since we have no real idea of the engines condition, only by what your saying, did anyone else at track look at your engine and tell your what they think of its condition? The hotter plugs run a thinner wire than cold ones, so maybe step down to a P4 or P6 plug and try it again. The thinner wire needs more fuel to keep it cool or they burn out. Also, if the compression on the engine is low or the piston/sleeve is worn out it will eat glowplugs also. I have run into this issue with O.S. engines and their hot plugs. Since the hot plug will stay lit more than a cold one, you won't really know the tune of the engine since it stays running till the glowplug pops. Also, if the glow plug wire breaks, you need to take the engine apart, because if the filament pieces drops into the combustion chamber, will will scratch the piston and sleeve. The colder plugs requires better tuning to keep it running, but I also get better speed out of the colder plugs on an O.S. V Spec. The RB & Novarossi turbo plugs fit, but are a bit smaller on the conical taper. The RB #6 plug seemed to work the best for us, but like I said, its a bit smaller on the taper, but thats all we had around at the time. I tried an RB#5, but it was slower. Try to get a colder O.S. plug and keep the same needle settings first and see how it runs. But like I stated earlier, if the piston/sleeve compression is low, then that would most likely be the cause.

only run the P3 OS plug, you could try the OS P4 at a later date but stick with the OS P3 for now.

check you have no air leaks, this will cause plugs to pop & make the engine hard to tune. also replace the fuel & pressure line.

never stop an engine by placing your finger over the stinger, this also will shorten the life of glow plugs.

if you do have a fair bit of slop in your rod, replace it just to be safe.

after doing all these go back to a rich setting on your top & bottom needles, & track tune only. do atleast 3 laps to get the engine up to temp, then start to lean the top needle 1/8th of a turn at a time, do another lap then repeat the same again.
Do not touch the bottom end needle until you have the top end right. the end result should be leanish on the bottom & just a tad rich on the top, just make sure you have a steady stream of smoke when your at the higher end of your throttle range.

last but not least, i would advise an oil content of no less than 12% in your fuel.