Buy a Sig!
Sorry, I couldn't resist!
Please forgive me.
How many total rounds are through the gun?
Can you describe the jam? Is it always the same (always first round, always last round, failure of slide to go fully into battery, double feed, always with just one magazine, or with any of your magazines?, etc)
Could be many factors so provide us as much info as possible.
I have read in various places that any 1911 with less than a Commander length barrel (4.25 inches) can be problematic with reliability, regardless of who works on it. On the other hand, Kimbers have a reputation for getting it right.
You say it always shoots great with hardball (I assume 230 grain hardball?). Try feeding hollowpoints with the same weight that have a hardball profile (Federal 230 grain Hydrashok, Remington 230 grain Golden Saber). If those feed flawlessly, then take a look at the profile of the ammo that is causing problems (bullet shape, bullet weight, +p load, etc). Keep accurate notes and stick to ammo that always goes bang. Isolate the characteristics of the ammo that causes problems and the situations in which the malfs occur and get on the telephone with Kimber -- discuss the facts with one of their reps.
Hope this helps!