ok, afraid that i had much more serious problems than a bad vacuum pump, i just went outside from work and pushed and pulled up and down on the crank pulley and couldnt get it to budge at all. i went from bench pressing the truck with my back on the ground to hanging my ~200lb weight from the pulley and it didnt move. even with belt tension, i'd think i'd feel some movement there.

so, hopefully its just that bad tensioner causing the belt to flap that was playing tricks on my eyes...

now i can feel better about spending my time and money doing the SD idler mod.