The only way to know for sure is to measure the opening, and measure potential ranges.

I replaced a slide-in with a free standing in my previous home with no problems (aside from removing that back piece of counter). The opening was just a bit larger than 30", so the side gaps were negligible.

It should be the same size, but not all slide-ins are the same. If the slide-in was made in the 1950s-late 1970s, you might find some unusual dimensions. The more recent ranges are usually standard sizes.

Thanks, ours is a 30" newer Jenn-air, so I guess we should be OK.

We found a good deal on a Kenmore Elite 5 burner gas range, but I am disenchanted with all Sears products right now (after problems with two washers).

I replaced a slide in with a free standing last month. To do so, I had to have someone cut the granite on both sides of the stove. I was very apprehensive, especially since a bunch of granite fabricators wouldn't take the job worried that the granite would crack. We found a great guy from Angie's list who did a very nice job, contained the mess and there were no damages. The gap is hardly noticeable.