In my experience the creation and maintenance of lag in the downswing has absolutely nothing to do with hanging on to it for as long as possible. In fact, it's quite the opposite.

The loss of lag at any point in the swing is down to the natural desire to hit the ball hard. This automatically tenses up areas of the body, including your arms, wrists, hands and fingers. Tightening up muscles in the arms in the swing only serves to straighten out the angles.

What you are experiencing is a natural response of your body to both your swing and desire to hit the ball.

Firstly, the task we've given our brain is to meet ball with club. Your body will adjust itself in order to achieve it, whilst at the same time trying to stay balanced. As a result, have a look elsewhere in your swing/setup to find the reasons for the loss of lag. For example, when I hit a weak one, I have a slight lean toward the target and target line (sort of diagonally left from a right handers point of view) at the start of my downswing. That causes me to manipulate the club in an effort to try and meet it square. The lag then goes as I have had to tense up certain muscles in order to manipulate the club.

A poor mental impression of a swing can causes tension and power leaks (including loss of lag). One point that I have not seen in golfing literature of late is the fact that with EVERY shot, we must swing through the ball. Let the ball get in the way of the clubhead. To do this, you must stay loose and free. So much emphasis now is placed on hitting the ball further, but the technique for hitting the long ball is the same now as it was 40 years ago. The equipment is what takes the ball to Mars and back in one blow these days.

Stay loose, stay relaxed, get a posture that allows the club to swing round you effortlessly, then put the ball in the way.

I guess this touches on why so many peoples practice swings differ from their actual swings at the ball. When you swing through the ball as if it isn't there, you get a connection that feels like proper control. You compress the ball. The feeling is that you can put the ball "there" whenever you like. It's a great feeling. Obviously with golf being the fickle game it is, that doesn't happen, but the confidence boost is huge.

Try to video your practice swing. I bet you get more lag later in the swing than when the ball is there. Then swing through the ball like it was a practice swing.

Hard to do but WELL worth the mental discipline it takes to do it. Without wishing to sound like I'm stroking my own ego, I hit a 3 wood yesterday on the range that CARRIED 275 yards. AND I felt like I didn't even try. It's surprising how far the ball can go when you let it.