The truck T-boned the driver's side of the vehicle killing Mr Stithem, aged 31.
Ms Steinke, 28, was flown to Waikato Hospital and last night remained in a critical condition.
The truck driver was uninjured but badly shaken.
The couple had been staying at Kiwi Paka Hostel in Waitomo for their honeymoon.
Police wanted to speak to the occupants of another vehicle at the scene of the crash.
The crash is the second fatal accident at the intersection this year and has residents calling for urgent action. Canadian tourist Michele Smith died after the campervan her husband was driving and a truck collided at the same spot in February.
Te Kuiti contractor Warren Finn said: "It's a death trap and we've known that for years but Transit [NZTA] aren't prepared to bend the rules so more and more people are going to die there ... it's a main road to one of the top tourist things in the country."
A resident asked NZTA to reduce the 100km/h speed limit to 80km/h on the approach to the intersection but was refused. "Unless they reduce the speed going past that corner there's always going to be accidents because tourists pull out and they are a little confused. You have to pull out very fast before you have a truck up your backside if they are going 100km/h.
"That's the difficulty, they are in a strange country, on strange roads, on the other side of the road and are very hesitant and slow moving."
NZTA state highway manager Kaye Clark said the agency planned to increase the road width adjacent to Mangarino Rd on SH3 and install a right-turn bay over summer.
Deadly corner
Crashes at the intersection of SH3 and SH37 from 2009 to 2012 involving foreigners
* Feb 2009 - serious crash
* Dec 2010 - non-injury crash
* Mar 2011 - serious injury crash
* Feb 2012 - fatal crash
* Sep 2012 - fatal crash.