I had a severe nosediving problem with an early 3rd generation G19. The problem persisted reguardless of which magazines I used, and reguardless of which followers I installed. I sold it to a friend of mine, and he has not been able to resolve the issue either.
The nosedives happened when hand-cycling, reguardless of whether it was the first round or the last round in the mag. It would also CONSISTENTLY nosedive when releasing the slide from slidelock on a fresh magazine (using the slidestop and using the "slingshot" method made no difference.)
I came to the conclusion that the problem was caused by the way the barrel locks in an upward tilt with the slide retracted, in order to guide bullets into the chamber. Under recoil, the barrel would tilt properly, but when hand-cycling or releasing the slidestop, the barrel would flop forward. This, combined with the lack of an intermediate frame-mounted feedramp between the bullet nose and the barrel's feedramp, caused nosedive jams. In order to prove this theory, I was able to consistently make it feed smoothly by putting upward pressure on the muzzle end of the barrel (making it tilt properly) while gently releasing the slide. For the record, I used hand-loaded cases with no powder or primers and Gold-Dot hollow points.
I know a lot of you guys seem to think that mag followers are the problem, but in my case, this was not true.