Just worked it out using 3.2 final drive and it comes out at 40.3mph/1000 rpm right on my 81mph @ 2000. Can you actually get the revs down to 1100 in 8th? you need to be on a neutral throttle not lifted off etc
If you put the Drive Select in 'E' (note that Drive Select is an option) then it is quite happy to cruise below 1100rpm in 8th... Or indeed if you take manual control it won't force a downshift until about 950rpm in my experience.
The tricky thing here is we are dealing with a viscous coupling - so the input/output RPM on either side of the box is not going to be exactly as per the ratios - unless the the lockup clutch is engaged making it true to the ratios... but let's assume that the lockup clutch is doing its job and engaging once you are cruising.
I will attempt 40.3mph and see what RPM I get on the way home!! I will also do 81mph and see what rpm I get...