Delayed D,R engagement with failed 1-2 shift

Hello Diagnostic Network,

I'd be grateful for help in determining next steps here. (Please.)

The vehicle is a 2000 Honda Accord 2.3L. JHMCG5675YC005231. BAXA automatic transmission, with about 90k miles on the car. 

I have observed delayed P-D and P-R shifts accompanied by the 1-2 shift neutraling. Heat seems to encourage these symptoms. Symptom onset occurred for our client after about 20 minutes of drivetime. I then had to put the car on the road for about an hour (this included a trip up and down the highway) before I got symptoms. 

Fluid (DW-1) replaced 40k miles ago. Done in multiple stages to the point that about 90% of the transmission's total fill was new fluid.

The transmission usually feels great. All shifts timely and clean, quick grabbing of drive and reverse, and lockup functioning. 

But with symptoms present, drive and reverse engagement were both consistently delayed. The vehicle would also fail to grab 2nd on the 1-2 shift. Delayed re-engagement of 1st gear would then cause a "bump" feeling after a coming to a stop. 

There are no DTC's stored. Heat seems to encourage symptom(s) behavior but not be absolutely required. I have gotten bad behavior at lower ATF temperature.

Under the delayed P-D (D4) shift, once the vehicle grabs 1st it can hold it, even under a hard acceleration. It will then either fail to grab 2nd, or just pull hard in 1st if driving with the selector in "1" range.

The delayed P-R shift comes with a loud clunk noise. That noise is not there when reverse engagement is not delayed.

The 1-2 shift will neutral and you'll get that bump after stopping, as 1st gear re-engages. The bump doesn't feel right and it's another example of the 1st gear grab being delayed.

Mainline pressure is in spec at all times during these symptoms. 120psi or better @ 1500 RPM, and that includes a fully warmed engine and heat in the ATF.

The vehicle can repeatedly exhibit all of those symptoms but then go back to feeling great after a cool-down/set period. I've put maybe 15 miles on the car since symptoms last presented.

I understand that the linear/CPC ("clutch pressure control") solenoids are important for achieving shift quality and feeding fluid to achieve gearshifts. They are mounted externally.

I'm not optimistic about being able to test solenoid operation effectively since I can't mimic the operating conditions of the transmission, and the transmission usually feels great.

I'm concerned that the linear/CPCS A solenoid is faulting. It is used to modulate pressure for N-R, N-D4, and 1-2 so a bad solenoid would readily explain all symptoms.

With that said, the CPC A valve looks to be in use for all three of these shifts as well. However, I believe it is fed oil differently when used for reverse than for N-1 or 1-2. If sticking, I suppose it could be symptomatic under different oil feed conditions...

Shift solenoid C is also in use for all three of these shifts. Since it remains ON for N-1, 1 (engaged), and 1-2, I consider it to be less of a suspect. (And again, the vehicle can hold 1st gear just fine.)

Per operation descriptions and application charts, I don't see any other components that have all three of these shifts in common. I am open to correction in that area.

Long story short: I'm not aware of a foolproof method to test the linear/CPC solenoids. Maybe I can pick something out by watching circuit amperage. I can capture scope waveforms. Tips? Please?

As I understand it, the CPC valves are in the valve body, and I don't think this valve body comes out without internal transmission disassembly. I wouldn't want to bill the client for a needless valve body pull anyway. I don't have a full understanding of this transmission's internals, and I know it.

I've seen reports of these CPC valves sticking on Honda products but don't recall much or anything that's BAXA-specific there.

I think I have strong leads on what's wrong given application charting, but I'm not all the way home.

I don't want to "convince" myself of what's wrong via reviewing application charts and miss a nuance of how this thing works internally.

I'm not inclined to "just try" a linear solenoid pack. It's a costly decision and does not suit our business practices. We prioritize figuring out what's wrong the first time and quoting a reliable price for a resolution. 

I have wiggled the axles and have not observed any severe play in the diff carrier area. Wiggle one axle and you don't see the other one move. Nor have I observed leakage from the axle seals. 

Your thoughts please? Thank you in advance.