Manual won't shift into reverse.

So my pilot bearing was grenaded so I pulled the tranny and replaced it with a new one. The clutch disc, pressure plate, and throwout bearing on my parts truck had more life on them than the current ones so I swapped those in while I was at it. Put everything back together and then it wouldn't go into reverse.

All other gears work fine.
Just put in a new slave cylinder like a weekend before.
Bled the crap out of the clutch system.
Made sure the shifter was in neutral before putting it back in. Tried the other shifter from my parts truck.
Drove around through all the gears.
Bled some more.
Gave up on bleeding and pulled the tranny again.

Grabbed the tranny from my parts truck and put the shifter on it before putting it back in my main truck. It seemed like it was clicking into all the gears including reverse, did the same thing on the original tranny and it went into reverse as well.

Put the parts truck tranny back in and then it didn't go into reverse.
If I hold the shifter really hard against reverse then the wheels spin backwards when I'm up on jackstands but it won't click in gear.
Tried spinning the wheels in the other gears then going back to reverse with no success.
Tried letting out the clutch a tiny bit before going into reverse fully but it still won't let me click it in.

Any ideas?

If the other gears work then the clutch should be releasing enough for reverse to work too yes?
The engine does idle down slightly when put it in gear with the clutch pedal down, is this normal or does this mean its still not releasing fully?

Only thing else I can think of is the clutch master cylinder crapped out at the worst possible time...

What if you shift into reverse, press down the clutch, and then start the engine? Will it drive in reverse then?

I'll give that a try tommorow. The shifter never lets me click into reverse in the first place though whether the engine is off or on. I think I may just need to bleed it even more.

My hypothesis is that the clutch is just on the edge of releasing fully, enough to be able to shift through the gears with syncros but not enough to get into the unsyncro'd reverse (or at least without a lot of force and at risk of chipping gear teeth). I may try getting someone to turn the back tires with the engine off while I release the clutch and try to get reverse to click in.

So I tried replacing the master, and adjusting the pushrod under the dash for maximum release of the clutch. When looking through the peep hole the diaphragm releases about 3/32", the throwout moves about 3/8". Tried starting the engine while holding the shifter against reverse and tried just feathering the starter without it fully starting just to crank the engine that wee little bit. Still wont go into reverse. I'm going to drive around more to see if it just needs to settle. Otherwise im going to have to take it to a shop...

Drove it around and the clutch pedal started getting spongy and the clutch was barely releasing so I think there is still air in there somewhere. Time for another bleed.

Did you find the solution to this problem? I have the same problem with the tranny I swapped into my truck yesterday, so I would love to know how yours is doing.

In case you haven't solved your problem, I solved mine! I just needed to put a spacer on the reverse light sensor! -simple and easy and I didnt have to pull the tranny