I have a 2007 suburban 5.3l 2wd that has recently had a used transmission installed into it the truck lost all power from sitting too long so I purchased a new battery and now it won't start I have spent months trying to figure out the issue but to no avail I have replaced the crank position sensor as well the truck will not crank by key but will crank by pressing the relay switch for the starter but still won't start I have hooked up a snap on bi directional scanner and found no issues the injectors have been all tested one by one and they are all firing manually and via cranking from relay I have spark also if you spray starter fluid continuously it will start and idle until you stop spraying I'm at a loss I also have a issue with the gear selection at times i have RND321 then when I adjust it I have PRND32 and also if I go under ander bump the natural safety switch forward a hair it will go in park also I have replaced the neutral safety switch I also forgot to mention that the bi directional scanner states it's trying to start in 3rd gear not sure why I apologize for how un organized this post is because I'm so scatter brained but I'm at a loss and I need help no question is a stupid question

 

If it starts and runs with starter fluid, but not without it, you have a fuel delivery issue. I would start by checking the pressure on the fuel rail, and go from there. Pressure should be up around 55psi with the key in the on position.

Likely suspects are the fuel pump (in the gas tank), the fuel filter, and fuel pressure regulator.

That said I just re-read and caught the issue with trying to start in gear. That could be the shift selector switch maybe? Or the linkage?