Odd 4t65 issue

[MattStrike]

in my '97 Lesabre 'l67 swap turned top swap'. Pulled from a 1998 Olds, unknown mileage, high enough that the 4th hub was on it's last leg.

Things it has:
hardened 4th hub
DIY shift kit
upgraded channel gaskets for the cover

And that's about it. No funky smells from the fluid, when I dropped the pan to change something in the shift kit I didn't see anything abnormal.

What it's doing:
When you get to the shift point, it feels like something is starting to happen, like power isn't quite reaching the wheels, but it takes over a full second for it to actually shift. When it does, it shifts like it has a shift kit. It does this on the 1-2, and the 2-3, and I think the 3-4. Thus far, I really haven't driven very far as the darn coolant elbow was leaking, and it need gas, etc, so I can't verify TCC lockup.

Kickdowns are instant, and it doesn't slip at all, WOT feels strong like you'd expect, aside from delayed shifts.

We messed around with the tune a bit, but it's definitely not that. At this point, I'm leaning toward something mechanical, or maybe it's something to do with the pressure switches, pcs, or shift solenoids? I was going to try and find the hydraulic diagrams that are not in any of my various CSMs. I don't have a tech 2 to do any scanning with, but I do have access to a DHP

All the engine sensors are working, the only check engine code is for the EVAP solenoid that I haven't extended the wires for (yet, doing that this weekend lol). I double checked the TPS, my scanguage is telling me it's working correctly and the DMM shows no dead spots.

My next diagnostic step is to follow the component resistance check procedure, just to see if I can rule anything out there. But I guess if I don't come up with anything I'm just going to drive it as is for a while, until the weather is mild again and swap in the other trans I have.

Any other thoughts or ideas?

[MattStrike]

OK, managed to find a PDF of the GM technicians manual for the 4t65. It looks like shifting on the 4t65e is really simple...

1-2 upshift
1. PCM turns off the 1-2 solenoid, which exhausts the 1-2 and 3-4 hydraulic signal
2. Spring pressure in the shift valve moves the valve to the upshifted position, sending fluid into the appropriate path
3. #2 check ball seats
4. hydraulic pressure applies the 2nd clutch.

2-3 upshift
1. PCM turns off the 2-3 shift solenoid, which exhausts the 2-3 hydraulic signal
2. Spring pressure moves the valve to the upshift position
3. #9 check ball seats
4. #4 check ball seats
5. Third clutch applies

and so on...

It looks like any kind of fluid pressure drop would result in either a slow shift or slipping. Bad solenoids result in a complete loss of a gear.

So at this point I'm guessing that there's either clogging in the shift solenoids so they can't exhaust properly, or the valves themselves are sticking slightly. But even that seems odd, how could both of them have the same issue?

[bs009]

PCS or pressure switches going out?

[RJolly87]

It's not torque management, is it? Or possibly false KR?

That's how I would have described my friends 2016 Sierra before it got a tune, like the computer was backing of power or slipping a clutch surrounding a shift.

[MattStrike]

Welp, this weekends recent events mean that I'm going to be putting the built up trans back in this car before I start driving it for the year. So if the other trans still does this then we'll know it wasn't the trans.