I do not think anyone was with Dulos in New Canaan because he needed MT to be in Farmington for his alibi to be anchored. AW2 also never says MT was with him in NC that morning, something I believe would be included in that warrant. There has been no indication anyone else was with him from either warrant, even though AW1 specifically puts MT with Dulos on Albany Avenue. Why not say she was with him in New Canaan also - unless LE believes she wasn't there. I also suspect at least some of the captured images have established to LE how many people were in the Tacoma.
I also am skeptical that Jennifer's body was left in New Canaan. Dulos, a guy known to be a speed demon, stayed strictly within the speed limit all the way to Farmington, which leads me to think Jennifer's body was with him. He was very deliberate in that speed. Maybe it was because of the items he still had in the truck from the murder, but I cannot see why he would keep them with him all the way to Farmington if he had already disposed of Jennifer's body. He could have easily stopped along the way to dispose of stuff if he didn't have a body with him.
The thing that bothers me most about the theory that Jennifer was left in a grave in NC, though, is the garbage dump on Albany Avenue. If Dulos had a grave pre-dug in NC, there would be no reason to remove her shirt and bra. He would simply have travelled to the site and buried her body and have been done with it. He didn't do that, though. Instead, he ended up on Albany Avenue. It makes no sense that he would have at least partially removed her clothes, but not have left them in that grave. Why would he create more work for himself that way? That dump is important and leads me to think Jennifer was in that truck on the way back to Farmington.
When I read that LE was in the woods behind Dulos' house, I speculated that it was because of some specific information MT provided LE. Others here believed it may have been the result of repeated tips by people in the community. Of course, then there is Dulos allegedly being seen by a neighbor in the woods with a shovel, but perhaps that is just more of Dulos being Dulos. We don't know why those woods are still being searched, but it has to be in connection with finding Jennifer's body.
In the absence of any evidence to answer the question, I go back to the drains. The AW are silent on this evidence and that is understandable. We will know a lot more once that evidence is released (or we learn there is no such evidence). If Dulos altered her body post-mortem, I think there is a likelihood he intended it to be incinerated, never to be found.
Obviously this is all conjecture on my part. We will know when it is the right time, but that garbage dump is part of the answer.