It couldn't be one of the bands could it? I know there isn't an external leak anywhere, but could one of the bands being out of spec cause that?

 

Only in manual first gear, I think.... If I recall correctly, with the shifter in D, the band isn't used for first, but, it is if you pull the shifter down to first. The other band is for reverse. (don't recall which is which either. ) But, if you don't get anything in any gear, with the trans disconnected..... you are losing pressure internally then somewhere. Might get a pressure gauge, and screw that into some of your test ports, see what ya get. (which port is which is detailed in the service manual.

 

Will do, thank you!

 

Pressure test is on the last page.
https://trucktransdiag.com/downloads...nsmissions.pdf