A/C on 170 Slant 6

Can a 170 slant do 60 mph with the AC on with 2.76 gears? Reason I ask is my sisters diesel rabbit had AC and when you hit that button, the speed dropped to 55 mph on the nose. No amount of pedal could get you any more. Wonder if it was designed like that or it was truly that gutless (52 hp?) pushing a brick at 55 mph on a 1.6 or whatever that coal fired plant was.