Eaton RTLO-16913A splitter question

I am having a tough time with going INTO overdrive (split) on my rig.
I split gears going up...5 then 5 over then 6 over...and so on.

We did the following to this transmission:

1. Replaced the shifter head and all of the air lines and fittings.
2. Installed the Eaton overhaul kit with new gaskets and o-rings.
3. Replaced the air governor on the transmission. Verify accurate PSI at the trans. NO LEAKS either.
4. Replaced the splitter slave unit.

Usually the biggest issue I seem to have is the 5 split. That's the 1st split I can make on the high side
of the box. I push the red button forward, remove my foot from the throttle - give it some time and then
hit the throttle again. Many times, nothing happens and I am in NEUTRAL at this point. It never makes/completes
the split and I cant figure out why. I find myself in NEUTRAL and the RPMs drop to 600 and thats how I know I am in trouble.

I don't seem to have this issue coming out of a split (say from 5 over back into 5).
Those complete fine.
I try to make all my shifts between 1300-1500 RPM depending...

I just dont know what else to look at....what's next to check here?

 

Actually I never pre-select a split. I hit the button in coordination of lifting my foot off the throttle......

 

I have had the oil changed twice (once about 3 months ago) to synthetic (50w I think).
It is full. No issues there..

 

Yea..its all good. Full PSI and a new air governor too.
Today I contacted EATON directly (tech support line).
They suggested everything I did already and then paused...

The splitter cover (K-3331) was redesigned about a year ago or so.
It now has a smaller orifice to permit slower and smoother splits. I guess there were some complaints.
So inadvertently, I may have made my problem worse.

The tech told/showed me how to use an allen wrench and remove the restrictor to restore the original performance (by opening the airway)
and also suggested opening things up again, and removing the piston and o-ring and inspect the chamber as well as lube up the o-rings.

I will be doing that next Tuesday. I am sure it wont hurt anything but if it doesnt help - there is nothing left to check.
Eaton told me at that point, the trans would need to be removed and worked on. (YUCK! $$$)
But I told the guy its only really the 1st split (5over) that is giving me issues and there is NO noise or grinding or anything nor
does it ever pop out of gear. So I personally think the trans itself is in fine shape.

It has about 500,000 miles on it at best guess.

 

I drained the trans today and totally removed the splitter assembly.
Cleaned it out and replaced ALL of the O-Rings including the splitter slave piston and replaced the splitter cover.

..I did have a small amount of oil where it didnt belong...

Total in parts was about $120 plus about 44 pints of Delvac.
So, now the trans shifts perfectly.