Didn't make it to the garage until about 9 (I had soccer after work). Ran the fuel pump with a line off the regulator straight into a bucket, and it acted the same as when the return was hooked up but not attached to the sending unit. So I'm quite confident that my return line is fine.

Pulled the sending unit out. Got the feed line apart at the sending unit (a day soaking in mouse milk and it was cake), and actually managed to get it off without ripping the rubber section. Since I really see no easy way of putting that piece back on, and I've already got everything apart anyway, I'm thinking of having the sending unit welded for -AN lines.

Took a look at that plastic piece where the fuel drains back in, and WOW is it small. Gave it a shot of air, and a little black something-or-other came out (I proceeded to burn it while cackling maniacally over the pitifully small flame). Again, since I'm already in there, I think I'm going to drill that little return hole out a bit.

Hopefully that was the issue. I won't have it ready for welding tomorrow, and my Thursday night is full, so it may not be reassembled until Friday...