Thanks very much for the advice. This pistol has only about 800 rounds through it since new in 1988, mostly fired int he last few years.
It's very clean.
No changes made to gun
The feed ramp is very smooth
No one has worked on it
Original mags are Colt and new ones same with metal followers
Mags are flush fit and not extended
Bullets are not set back
I also found that by using a thin screw driver to force the second round from the top of the mag to the rear as I load each round, the rounds seem to cycle through okay. I don't know why all mags would start doing this unless it's something else I can't see.
Side note: Hornaday's Critical Duty will not feed at all and never did before I had this problem. As this round starts to move forward hitting the ramp, the slide somehow cocks the round in a front down position against the ramp (possibly hanging up on the bottom of the ramps edge) with back of the round cocked up slightly preventing the slide from continuing forward.