New...ish aveo owner

Hi all Im new here, names Steve, Im from Quebec Canada and have been following this forum for quite some time as a visitor and now decided to become a member. I bought a 2005 aveo about 3 years ago and everything was fine until about 3 weeks ago when the pulley broke and spun the timing belt!! I was able to get a 2006 motor with only 50k on it so I put it in (had to put my original intake on it) and after we hooked everything up it started but revved really high like 5 grand. After a few tweeks it ran a bit lower 2-3 grand. A mechanic told me to take it for a ride and maybe the computer would reprogram, so thats what I did. When I got back home I shut the car off and it wouldnt start, had spark and had fuel at the rail but the injectors were not pulsing. So I read a post on this great site that said the temp sensor might be bad so I put the one in from my old engine and the car started.......buuuuuuut after taking it around the block I shut it off and once again it would not start. Now I noticed the car was hot and my fan did not kick on...the guage in the car stayed at half and did not indicate the car was overheating but I could feel excessive heat from under the hood so something is not registering somewhere....tomorrow Im gonna make sure my fan is still good and check fuses but other than that once again I am puzzled!!! Any other advice would be awesome!!

Thanx Steve