I'm having issues when gas tank is at quarter tank, its like i have no power. But when its at full tank no issues at all or lights. Then i get engine line comes up and transmission starts doing odd stuff. I just wondered why i'm getting transmission codes when sounds like fuel pump is going out?

05 G35 infiniti sedan stock everything.

 

Sometimes a component can be failing which causes a malfunction in OTHER systems. For example here's a hypothetical situation.

Fuel pump begins to fail, sends reduced fuel flow to the engine, engine doesn't send correct torque to the transmission, transmission doesn't build adequate pressure to properly work, TCM is expecting the hydraulic pressure so it's sending the transmission through the gear it should but eventually the TCM decides something is wrong (shift control solenoid error code P1762) and lights up the dash and limp modes the vehicle.

Now the problem originated at the fuel pump in this hypothetical situation but the FIRST COMPONENT to actually see the problem was the transmission control module so it sent up a diagnostic trouble code because part of its system is not working properly.

First thing I would do is start logging milage of the vehicle, if you start experiencing these issues at about 400 miles into a tank of gas yet it shows that you still have a quarter tank left then you probably have a faulty fuel sender and are running the vehicle down to it's last gallon of fuel. Next thing I would do is check out the factory service manual online, it starts at the FWD.pdf section, go to FUEL and perform all the steps to troubleshoot the fuel pump without removing it from the vehicle. Next I would install a fuel pressure inlet port on the fuel line so you can actually read pressure at the injector rail to verify there isn't a fuel delivery problem since the problem is REPRODUCIBLE at a certain fuel level.

If all those things check out then start your focus on the transmission, how many miles are on it? When was the last time it was serviced? If there's 150k on the tranny and it's never been serviced then yes you probably have a huge problem and might need to replace it from not following maintenance REQUIREMENTS (not guidlines or suggestions). If you don't have the neccessary tools to repair an auto trans then it's probably best left to a reputable shop that specializes in them. The dealership can perform a thorough diagnostic for a reasonable price to determine if the valve body in the transmission is shot, it's about $1k for just that part not including labor.

Now this next part isn't directed at you so don't take it personally:

Ok end rant, I hope the problem isn't actually your transmission.