This is just a shot in the dark, but mods generally pop out of temp mode when the resistance of the atty goes above a certain value. Doesn't have to be for very long, even a few milliseconds. Since the problem has been tied to the 75w pico more than other mods,
maybe it's because the tip of the V5 atty is just barely touching the center conductor in the 510 connector in the pico. This is just a thought; I have no evidence of this (and I don't have a pico to try things out). If your V5 works fine on other mods, it's probably not a lose connection to the cup wires (so don't over tighten the hex screws too many times or you may break the cup wires).
I don't know if "wrenching" down the V5 when you attach it is a good idea, but maybe putting a thin conducting piece of something metal on top of the center conductor in the mod would work. Like a tiny piece of aluminum foil folded once or twice to make it thicker. You would have to
make sure the foil isn't wide enough to touch the outer conductor (which would present a short to the pico). I envision putting a 1/4" circular piece of foil in between two pieces of clear tape, with a hole in the tape on both sides to allow the foil to contact the pico center 510 conductor on one side and the center conductor of the V5. The tape would prevent the foil from sliding around and touching the sides. I have a couple of 510 "extender" adapters (male 510 on one side, female on the other) that I've used to test a suspected short 510 connector on a different mod and atty. If you happen to have any around from the good-ol-days when half the atty's wouldn't connect properly with half the mods, this would be a safer test to see if a too-deep 510 center conductor in the pico is really the problem.
Or maybe this is a really stupid idea and you should just get a different mod... I have great success with a couple of Joyetech eVic VTC Minis, one for the V5 beta (which still works fine) and one for the V5 release. I also used the VTC Mini with great success with the V4 and the QQ and others before them. 100% Arctic Fox compatible. They're on sale
here for $29 (with an e-juice atty you can probably just give/throw away).
Haywood