Glad you have it resolved and are able to shoot it without issue!Update to my magazine issue. (post #13) In addition to sanding the baseplate as I described. I also installed a stronger magazine catch spring, sourced from Numrich. It was for a Sig P938 and is about 1/8" longer than the stock Kimber spring and fits with no problem. The mag clicks in more securely and the mag release requires a slightly stronger push to release the mag.
Finally made it to the range today and problem fixed! Fired 50 rounds each of Federal and Blazer 124gr FMJ with both the original 7 round mag and the Tac-Mag Kimber sent for free for a sales promotion. The mags stayed securely locked into the gun and didn't have any malfunctions of any kind. I like the 7 round Tac-Mag a little better that the regular 7 rounder because of the slightly more pronounced pinky extension it has and it is easier to load as well.