1991 Suburban R1500 shut off completely while driving

[Acostaburban21]

I have a 1991 Subruban R1500. Was driving on the highway and the truck just shut off. Now I can’t get it to turn on. No dash no crank no radio. Lights work. Windows don’t. Checked battery it’s good checked alternator it’s good. Went through fuses and can’t seem to find any issues. Any other suggestions?

 

[zora]

What is the exact battery voltage?
How did you check alternator if it doesn't start?