[Vwdiesel] Rabbit Shift Points

[Bryan K. Walton]

I've been trying to figure out where the optimum shift points are on
my '84 Rabbit with the 4A four speed transmission in order to help
maximize my fuel economy.  I have an upshift light that comes on
at various speeds but I'm not sure exactly if it is coming on at
the correct time. The reason I question whether it is functioning
correctly is that it used to light up at the following speeds:

Shift into 2nd at 9mph
Shift into 3rd at 18mph
Shift into 4th at 27mph

I noticed that when I shifted at those speeds, the engine sounded like
it was lugging (especially when shifting into 4th).  Then, in January
I replaced my injection pump and set the timing to be within spec, but
retarded.  I got everything back together and noticed, bizarrely, that
my upshift light was now coming on at different set of speeds!?  It
now lights up as such:

Shift into 2nd at 14mph
Shift into 3rd at 25mph
Shift into 4th at 37mph

Using these shift points, the engine definitely is not lugging. 
But now I wonder if I'm shifting too late -- if the RPMs are getting
too high.  I don't really know.  My guess is that these points are
closer to being correct.  The gear ranges listed in my owners manual
seem to coincide more with how the upshift light is working currently.

1. Can anybody suggest how changing the IP and its timing, could
possibly affect when the upshift light comes on?

2. Can anybody tell me at what speeds the upshift light should turn
on, with a 4 speed transmission?

3. My speedometer has some "dots" on its face at various speeds.  
Specifically, the face has 1 dot on it at the 23mph line.  It has 2
dots on it at the 43 mph line, and it has 3 dots on it at the 68 mph
line.  Can anybody tell me what these dots mean, if anything?

Thanks!
Bryan Walton