Long story short, I just finished rebuilding my 4R100 in my 2001 F-350.
I purchased a master rebuild kit from transmission bench, along with the Transgo HD2 Tugger kit. New cooler was installed along with a new torque converter. Mechanical diode was deleted and replaced with 45 element sprag. New (remanufactured) shift solenoid body was also installed.
Got her filled with fluids this evening and backed her out of the garage. All seemed good. Drove 1/2 mile down to the corner stop sign, shifts were nice and crisp with no issues. Went another mile to the next stop sign. All was good. Took off from the 2nd stop sign and the transmission did not want to shift from 1st to 2nd.
I would have to get the RPMS up and then let off the pedal before it would shift. Once in 2nd, all shifts were fine.
My hunch is a sticking valve in the valve body. One of them was stuck when I tore the transmission down. I cleaned up the bore until the valve seemed to move freely but perhaps it wasn't enough. Honestly, I'm not even sure a sticky valve would cause my issue but I'm hoping that is all it is.
If anyone has any ideas, or at least a list of what can cause a delayed 1-2 shift I would appreciate it. At least it would give me a place to start looking.

Thanks,
Jon

 

One or more of four things typically cause this.

Sticking valve in valve body (you already claim to have fixed).
Broken spring in accumulator.
Warpage of seal surfaces between center support and case (Sonnax makes a kit with rubber tubes to negate the metal to metal seal).
Did you use the shim washer between the center support and the case (Sonnax makes those too).

I have experienced/fixed a lot of each of these problems. I have used both varieties of the Sonnax parts numerous times with good results. Three of them don't require more than valve body removal to accomplish but the shim means dropping the transmission and removing everything down to the center support.

 

Sounds reasonable to me on the sticking valve or solenoid.
Either it’s not being commanded to shift or something in the VB is preventing the shift from occurring when it is commanded.
Do you have a way to watch the PCM desired gear? On the CTS you can have it display what gear it’s in. If the display changes but the transmission doesn’t shift then that would point to VB.

I’m not familiar with what the PCM looks for to shift but it does have speed sensors in the trans and rear end. If the PCM isn’t making the command then I’d look that direction.

I’m sorry for my poor support here but wanted to at least give you a bit of feedback since no one else has shown up yet.

Edit: Cleatus posted good information while I was typing. Might be best to disregard my comments.

 

I dropped the oil pan and pulled the Accumulator valve body.
At first glance everything seemed fine. All valves snapped back when I moved them with a pick. After cycling the accumulator valve a couple times, it stuck in the bore. I pulled it apart and cleaned up the bore as best I could until the valve seemed to cycle fine. Put it all back together, but the problem still exists. Not sure what to do at this point. I believe this is 3 of the 4 valves in the valve body that have been sticky for me. Would it be worth buying the Sonnax bore sizing tool to properly clean up the bores, or should I maybe just look at picking up a different valve body?
And yes, I did install the shim between the case and center support when I installed it.

 

Dropped the transmission out this evening. I had a hunch I knew what might be the problem.
The transmission was shifting just like the intermediate sprag was shot. I had replaced the mechanical diode with a traditional sprag. Problem was, I replaced it with one of those kits that converts your existing clutch housing drum from a diode version to a traditional sprag design. It appears there was a lack of lubrication to the sprag gear. All of the inner teeth were worn flat, the thrust washer was partially melted, along with the thrust washer on the center support. At least I know what the problem is. Now to find a replacement drum and do it right.
Thanks to the guys that replied. Certainly was hoping it was something simple, but I had my suspicions.

 

Glad you at least found the issue. Sorry it means more work for you.

Are you certain the sprag was put in the correct direction?

 

Outer race would rotate counterclockwise when installed. Locked when trying to move it clockwise.

 

Did you just replace the sprag and put it back together and everything worked?

 

I had to source and find a different clutch housing drum with a new sprag. The clutch housing drum I used was a non mechanical diode version unlike my original.
After replacing and putting it all back together it's been running great.
25,000 miles and no problems.