Hard shifting in a NV-5600

[DLangford]

I replaced the clutch, pressure plate, pilot bearing and had the flywheel done last spring in my truck. Everything was fine until a few months ago when I started to notice difficulty getting into a gear from a complete stop from neutral.
Reading here on the forum it sounded like my clutch slave was most likely the problem.
My neighbor, who is a professional mechanic, came over and looked at the clutch slave, he could see where it was leaking a bit. The clutch master looked fine, no leaks and plenty of fluid.
We decided to replace the slave cylinder. We got one from Napa.
Installation was not easy since there is no bleed valce on the slave making it hard to get all the air out, especially with the way things were tilted in the assembly process. We finally got it bled and I noticed an immediate improvment in ease of shifting. However, one week later when I drove the truck I found I was back to square one.
Could "new" residual air be involved here? Should I have bit the bullet and got the more expensive Mopar fix which is the clutch master and slave connected and pre-bled?