Small change, big difference

Grip change still working, had good ball striking both Sunday as well as today.

Your grip can change your swing completely.  I'd say it is the third most important mechanic to a golf swing, behind swing plane, and head movement.

Proper Grip is one of the last things, unfortunately, that I focused on. I had many lessons from extremely poor excuses of "professionals" who never stressed the importance of grip.

I found out long ago that I was actually using a very weak interlocked grip with my left hand too far "under" the club in a weak position (I could not see any knuckles on the top of my left hand).

Since putting my left hand farther right on the grip and being able to see 2-3 knuckles, as well as straightening my right arm out (strong grip), I hit a slight draw with all clubs. I went from a 20-30 yard slice (left to right) to a gradual 5-10 yard draw from right to left. This easily increased my FIR substantially.

I kind of disagree. I think it's "up there" on the list of the most important swing factors. To start off with, a weaker grip could definitely promote a slice or lack of control of the club face before any other factors or mechanics of the swing as a whole begin.

For example, a weak grip with the shaft crossing diagonally through the palm rather than properly across the last knuckles of your fingers (at the base of the fingers) could cause the club face to remain open, to spin/move on impact. Would it be "impossible" to hit a good shot like this? No. Is there a good chance that the majority of an amateurs shots with the described grip are going to be sliced, uncontrollable, or simply produce unwanted results? In my opinion, absolutely.

I have been fighting pulls/hooks most of the season. Last Friday I decided to go back to my old grip (which is much like you describe in your original post) and I have been much more consistent since. It's not a big enough sample size yet for me to say it was a leading cause of my problem but early indications are encouraging.

When I started playing again in April, I developed some pretty bad pain in my right forearm. I was surprised because even though I hadn't hit a ball in six years, I've never had a golfing injury, and I've hit a gawdawful number of balls. I finally took a hard look at my grip. I was placing my right hand much more under the club than, for me, it should've been. As soon as I rotated it back to the left, no more pain. In addition, I started striking the ball much better. I know people have success with all types of grips, and I'm not saying that the grip that hurt me was "wrong", but it was wrong for me. It was pretty key, or important, for me. Ymmv....

In before Iacas changes "grip" to "club head control" and changes it to the 5th most important mechanic :)

I certainly not the golfer as the other comments above are, but to me the grip is perhaps the most important thing in the golf swing.  I know in my case when I change grips it changes my setup and swing plane (I've seen the videos).  In my personal case I try to keep my hands on top of the club (neutral grip pretty much, with a medium left thumb going down the middle of the shaft and the right hand life line over the left thumb, interlocking grip) and that seems to work the best for me.   But I would encourage everyone to experiment with their grip and see what works best.  What is good for the goose isn't necessarily good for the gander when it comes to grips.

I think importance of grip depends on swing style. I'm normally a hands and arm oriented player and grip, especially right hand is hyper-critical.

When I try to make a more body oriented swing I find that grip is not so important.

I believe I see the same tendency in writer/instructors.

The handsier the swing recommended the more grip is stressed.