I have rebuilt the transmission and I am having a low pressure problem.

The reason for the rebuild is that I didn't have reverse. Drive was strong and worked perfect in all gears. I first lengthened the servo pin (thanks to a tip from this board) but it was a temporary fix so I decided to rebuild. Once inside everything was as I thought it would be. The bands were very worn.

I did not replace or build the oil pump or torque converter.

Symptoms -
The truck drives perfect until it warms up, then the transmission feels weak and like it slipping in all gears.

I wet air tested the trans and all gear engaged perfectly.

I hooked an pressure gauge to side of the trans and I get the following readings...
When it was cold (on jack stands)....
Park 55-60 psi
Drive 50-150 psi
Reverse 55-150 psi

Once warm....
Park - 0-5 psi
Drive 0-10 psi
Reverse 0-10 psi

There is no service light but I reset the computer (unhooked both batteries) then drove it till it was warm and showing symptoms.

I get the following codes...
24 - VSS circuit
81 - 2-3 shift solenoid
82 - 1-2 shift solenoid
83 - TCC PWM Solenoid Circuit (Automatic Transmission)
84 - Accelerator Pedal Position (APP) Circuit Fault
87 - High Ratio Error
99 - Accel Pedal Position (APP) 2.5 Volt Reference Fault

Since I have been experiencing the current problem I replaced the throttle body and everything inside or attached to it (all from a donor trans...everything was identical) but the the symptoms did not change.

At this point I think it is an electric problem. I am not sure how to proceed troubleshooting it at this point.

Any ideas?

I get the following codes...
24 - VSS circuit
81 - 2-3 shift solenoid
82 - 1-2 shift solenoid
83 - TCC PWM Solenoid Circuit (Automatic Transmission)
84 - Accelerator Pedal Position (APP) Circuit Fault
87 - High Ratio Error
99 - Accel Pedal Position (APP) 2.5 Volt Reference Fault


I believe your reference voltage should be higher. I am not exactly sure of the range but I am guessing ~4.7-5.0
I believe high ratio error and VSS fault are cousins reported by the computer.
I think you have an electrical fault for sure. I am surprised the PCM didn't register low voltage.
Lets think about grounding. All grounding should be squeaky clean Removed wire brushed and replaced. Check the grounding from the battery to the body. Check Grounding from the back of the engine block. Check grounding from the computer. Check grounding everywhere.
An alternator is an electron pump. It has a positive and a negative. A battery can be considered an electron pump. It has a positive and a negative.
Corrosion along a wire, at a terminal is considered to be pressure loss or Voltage drop. Voltage is pressure.
It is cold outside and cold weather compunds the ability of charging and holding current.
Amperage is volume of electrons moving from point A to Z. I term it Capacity and Volume.

Check and see that the computer is receiving the correct voltage and grounding.

A good place to start
Disconnect the passthrough connector and check pin E for voltage. Turn on the ignition key to power up the truck but don't start.
You need 12 Volts Direct Current. Select a good chassis ground.
If you are receiving lower than normal voltage than I suspect a poor grounding issue.

A good place to start
Disconnect the passthrough connector and check pin E for voltage. Turn on the ignition key to power up the truck but don't start.
You need 12 Volts Direct Current. Select a good chassis ground.
If you are receiving lower than normal voltage than I suspect a poor grounding issue.

I tested E and it looks good. The voltage is exactly the same as at the battery.

I proceeded to clean up all the grounds.

When I tested it did the same thing...ran perfect when cool then the pressure dropped once warm.

Then I disconnected the plug from trans just to see if the truck would throw different codes....but surprisingly nothing changed. The truck acted exactly the same. It is like the trans doesn't care if its hooked up the computer or not.

Piglet: A strange problem indeed.
DId you put in the right type of transmission fluid?

We need to figure out a few things.

Electrical

or

Hydraulic

I might believe you have both.

I am a betting man your pump is not pitting out the pressure it needs to.

Did you experience this before you changed out the torque converter?

Did you place undue stress on the pump splines when reinstalling the transmission?
Did you use a transmission jack or did you and a buddy muscle it in?
Get a pressure gauge and hook it up to the left side of the transmission. A gauge that is rated with enough bars to handle 350 PSI american.
With the transfer in neutral run the transmission in all forward gears and reverse.
The forward gears should register ~90-120 PSI.
Reverse should register 270-300-320 PSI.
Let's see about hydraulic pressure first.

When it was cold (on jack stands)....
Park 55-60 psi
Drive 50-150 psi
Reverse 55-150 psi

Once warm....
Park - 0-5 psi
Drive 0-10 psi
Reverse 0-10 psi

Low pressure problems now that you verified your issue.

Internal leaking

Improper control valve operation.

Slipping or failure of clutch packs. This can show up as a loss of a gear ratio in DTCs

If your Torque converter was not engaging or slipping back out of Overdrive I am venturing a guess control valve operation or it's enabler valve function. It very well could be shot.

Clutch packs? Yes clutch packs. They have seals to pistons. They engage and force application to clutches. If those seals are unserviceable then you need a rebuild.
More than likely a rebuild is in order.

We just did a rebuild.

The reason for the rebuild is that I didn't have reverse. Drive was strong and worked perfect in all gears. I first lengthened the servo pin (thanks to a tip from this board) but it was a temporary fix so I decided to rebuild. Once inside everything was as I thought it would be. The bands were very worn.

I did not replace or build the oil pump or torque converter.

Symptoms -
The truck drives perfect until it warms up, then the transmission feels weak and like it slipping in all gears.

I wet air tested the trans and all gear engaged perfectly.