42RLE slipping on take off in first gear

[JPHikr]

42RLE slipping on take off in first gear.
2005 TJ Unlimited Rubicon 145k miles.
Derale 20561 Trans cooler along with Two Derale frame rail coolers mount on the grill.
When it is cold there is no slipping but once I drive it, it will slip on taking off.
Trans works fine in the upper gears no slipping.
I was have the torque converter problem not locking up when really hot out 110 plus during the summer.
Caller wrangler fix had a ecu sent to me after talked to Mark.
Installed but it did not solve the problem. I sent it back Thanks Mark great guy.
More studying up on it found the a worn valve body can cause this.
So I got a ATS replacement valve body and installed it.
Then I got the slipping in 1st when taking off.
Replaced the input and output speed sensors.
Have checked the shifter adjustment and it is correct.
Atf4 is just above the full mark when hot.
Any Ideas on why I am getting slipping on take off in first gear

 

[hear]

Slipping is pretty much always an issue of the clutches being worn too much to grab and/or there being insufficient pressure to apply the clutches.

Since you said it started right after the valve body swap, I would immediately suspect a bad valve or similar. I think I would put the old one back in and see if the slipping goes away. Then you can isolate if it’s the valve body or something more internal.

 

[JPHikr]

I sent the old valve body back to ATS.
So cant do that.
I works fine on the first shift then slips.
The TC locks up not slipping in 2,3 or 4th gear.

 

[JPHikr]

It is showing P0731 code.

 

[hear]

All signs kinda point to the solenoid. I'm just kinda throwing darts here, but this doc shows you how to ohm out the varioius solenoids. Maybe see how that looks and report back?

https://atracom.blob.core.windows.net/bulletins/2013/feb/atb1513.pdf

 

[JPHikr]

I put a new ATS valve body and soleniod in it.
There is no way to check it in the Jeep without cutting the tunnel for access.

 

[hear]

 

[Dylan_See_TJ]

Cutting the tunnel? ...The valve body and associated parts are accessed, from, y'know, the pan... on the bottom... and the pins are on the top, sure... but unless you've got some weird mods that reduce the space between your tub and your drivetrain, you should be able to reach up in there. Not saying it'd be fun, but slipping in 1st is slipping in 1st.