Originally posted this in the E39 forum, moving it over here in hopes of more eyeballs.

I'm attempting to complete the transplant of an M54B30 and its ZF 5HP19 into my '03 525iAT. Build date of the donor 530i was 5/03. Everything's in the wagon, hooked up, I flashed the DME and EGS, all of that's gone smoothly. After troubleshooting a couple of vacuum leak issues that I caused during reconditioning, the engine's running nicely. With the engine running, I was able to finish filling the transmission fluid, and that's where I've hit the wall.

The car moves forward in D, stays put in P, rolls a little in N...and goes forward in R.

I got too big for my britches and did a partial rebuild of the transmission while it was out. I replaced the torque converter and oil pump, all of the friction discs, and most of the O-rings. I didn't do anything with the valve body other than to remove it and put it back.

The donor car had 163K miles (wagon body has 246K), and I'm not really sure why I decided to do this rebuild, other than that there had been some very minor slipping, which could probably have been mostly addressed by a fluid change, maybe by replacing the torque converter. Honestly, everything inside the transmission looked very clean and most of the O-rings I replaced were still pretty supple.

I'm assuming I did something wrong during reassembly to cause this? It's not the usual "reverse issue" that most 5HP19s have (my D/G drum was fine, it's a later production date than the ones that usually fail anyway, and the car still moves in reverse, just in the wrong direction), so I'm not finding any information on what could be the problem. The EGS hasn't thrown any codes.

The other thing is that when I shift into R, there's a hesitation, where it feels like the car is building up pressure (?), as if it's trying to figure out what to do, before it starts to move forward.

I followed the usual fluid fill procedure, and since the TC was new, it took a lot of fluid (over 10L)—I had the car running at temp, the transmission warmed to 40C, and filled until fluid streamed out—so this couldn't be as simple as low fluid, could it? Do I need to look at rebuilding the valve body, even though as far as I can tell it was fine before?

Thanks for any insight into whatever boneheaded thing I've done here.