Hi, and thanks in advance for any help/advice.

We installed a brand new 4L70e with an LS3 crate engine in a 1951 Chevy Truck.

We drive no more than 20 miles, doing testings, and is brand new transmission.

Randomly but mainly during cruise when I accelerate and the transmission need to down gears, it goes to 1st gear and doesn't shift up. I need to stop, and then transmission works fine. Sometimes the problem appears without hard acceleration.

I checked:
- VSS Signal: when the problem occurs, the speedometer continuos measuring. The speedometer is a DAKOTA DIGITAL and is connected to de ECU output speed signal wire.
- Checked fluid level: ok
- No DTCs detected
Here I have the first doubt, because even if I unplug de VSS none DTCs is setted.
- Connected to the Transmission Controller using the Chevrolet Performance Software provided. I did a couple of datalog sessions, and the info that the datalogs files show is very confussing to me. When the fail appears:
. Transmission goes to 1st gear.
. VSS and ISS signals show 0.
. The speedometer continuos reading.
. TCC lock works fine (The Software show the TCC Lock indicator in green when it activates)
. TCC Slip Speed is equal than Engine RPM. For example: 2500 RPM, VSS = 0, ISS = 0, TCC Slip Speed = 2500.

Please see attached a couple of datalog files.

Thanks again for your help.