Just dismantle it and make sure there are no deep scars where it slides and that is has no play.

Also, you said there are codes in the ECM. This car locks down 4th for a lot of reasons. Such as air suspension.

Check whole car.

 

Did you replace the solenoids ?

edit, just re-read that you did replace them.

 

Alrighty update here, I got and ran the full rebuild kit, and replaced all the frictions and plates, and most gaskets and seals. went together really well, everything was tight and spins pretty well. Turns out the plates and frictions for one whole gear was were completely destroyed, some in many pieces.
Things I replaced outside the transmission rebuild:

• upper and lower O2 sensors, MAP, and MAF.
• gas tank (the old one was not giving the gas level)
• front driveshaft
• rear main seal
• torque converter

But after getting everything put back together (took about a month in my free time) I can't start the thing. Out of nowhere the starter just isn't even clicking on. basically single click and complete silence, worked fine right before all this.
tried the hammer tap.
The flywheel can spin freely (with some effort) from the harmonic bolt.
Electric looks to be seated well, double checked the connections, no issues.
The battery seems good have a battery charger, and got it to full.
I'm honestly not sure where to go from here haha. Any thoughts on what might cause this? is it really a bad starter?

 

mmhmm, sounds like you did not plug in the transmission plug all the way in?

Have someone mess with starter while you wiggle it.

 

I agree with MyChocolates…

I would take a good read through this thread and closely inspect your transmission electrical connector.

https://landroverforums.com/forum/lr...-start-113819/

 

Alrighty, I unplugged it and cleaned it out with an electrical contact cleaner, checked the pins and they looked good from what I can tell. I made as sure as I can be that it was seated all the way, it doesn't wiggle at all. had my wife try starting it while I wiggled the wires and pushed on it. I can scan it with my iid tool when key is in and returns details of the transmission ECU, but I'm not positive that's coming from the actual valve body ecu there or somewhere else.

 

This is easy to overlook.

 

This is a common one too, making sure the linkage is properly engaged. I almost made this mistake and caught myself before full reassembly.

Forgive me if I’m overstating the obvious. Just sharing experience while trying to help.

 

Thanks @P-Bod
There totally is a gap there from the first picture, it smells like its not all the way seated? =(
draining now.
I'll double check the second picture there as well.

 

Alrighty! had a spare sleeve, and plopped that in, and voila, was able to start!! filled the trans fluid back up and I took it out for a small test spin around the neighborhood to test the rebuilt trans...
Unfortunately, now it doesn't have second gear.. took it for a few laps, just to make sure fluid wasn't an issue... no dice.. holey butts... boy am I extra sad =(.
Everything in the valve body looked good, all fresh gaskets, placement for shifter (above) is good.
When rebuilding the trans I mostly replaced the frictions and plates, a few of the loose metal seals, and accessible gaskets, from everything apparent, it went really well. no cracks, no visible leaks, going back together was a little challenging to get all the plates to align right, but nothing too crazy, just time.

I'll keep playing with it, but I'm guessing something I did with the rebuild is causing this. Unless there is a clear reason this would happen, at this point I want to throw my hands in the air and get a professionally rebuilt trans before dumping any more time/money in =(. It was worth a shot, but I'm in over my head I think. There are nuance's on nuance's that may not be apparent to me with these things.

I do appreciate everyone's help here, I'm learning a lot and enjoying the process either way =).