Hwy 90 is the fastest, easiest and scenic route from Jerusalem to Tiberias.
From Jerusalem take hwy 1 east to Ma'ale Adumim and the Dead Sea. Continue all the way DOWN (probably the most efficient road in the world - you travel at 100kph (62mph) without even touching the gas pedal...
When you get to "Beit HaArava" junction take left to highway 90 - signage will tell Beit She'an and Allenby bridge and "90". From there - easy all the way north (one checkpoint near Beit She'an) pass through Beit She'an straight, signage will begin to point north as Tiberias - 30 minutes from Beit She'an and you're at Tiberias. All in all I estimate 2.5 hours.
And a remark - hwy 6 is a toll highway - but an electronic toll kind. That means there are no booths - you just drive and the cameras take your car license plate number, and ship the bill to the car-owner address at the end of the month. Since your'e renting - that would be your rental company. That's why some rental agencies will tell you not to drive hwy 6, and some will bill you when they get the bill from hwy 6 + "handling fee". For the sake of information, the exit to Tiberias from hwy 6 is Ein Toot interchange (the northmost one), then hwys 70 -> 722 -> 75 -> 77.