Crazy rollercoaster ride

[Bogeysaurus]

Has anyone else experienced the following:

I recently discovered a couple flaws in my swing that I am working on fixing.

The last 3 times to the range the same thing has happened.

I start with 1/2 swings and I'm hitting brilliantly.  I maybe hit a few 3/4 swings but not really trying to crank on it just get used to the feel of proper swing and impact.  After a dozen or so great shots I'll eventually hit a fat shot or slice it.  Fairly quickly I'll get back to hitting good shots but maybe only 8 before the next screw up.  Each time though eventually the slicing/shanking gets worse and it gets harder to get back to hitting the ball properly.  I then struggle to get one or two final good shots to leave the range on a good note.

What is the deal!  I start off great and the longer I practice the worse it gets...  Each time I think AH HA so that is the difference in feel when I hit a good one and bad one so now I know what to do.  But by the end every swing feels the same and my muscles feel numb to any small changes.

Don't know what to do... just don't know how I am supposed to build consistency or muscle memory if each time I start great and end bad without any sign of progress.  Is this just the nature of slow progression of a golf swing?

Thanks