LS376 and 4L70E

[SeabeeJamie]

Learning this stuff the hard way....

I have a LS376/495 Crate from Summit, originally tried to mate this with a 2002 4L60E (No ISS). after some bad advice that this will work, It will not, not correctly. Shifts are too hard. not looking to build a race car, just something to go out in on Saturday nights.

E38/T42 ECM/TCM, as of last night I now have a 2007 4L70E (15 pin) in the car. about to change the wiring, does anyone have a recommendation for a good year base tune for this set up? Bosch MAF, shift kit in the trans but want to keep trans tune stock (as per builder), no mods done to engine. Even went with cast iron manifolds (ceramic coated). 2009 Silverado tune had idle issues, but this may have just been due to the codes being thrown (wrong internal state) by the non-ISS transmission.

[Shrek]

It is helpful in threads like these, if you post your current tune, and describe where the wiring harness came from. Quite clearly, you are not using the CPP (GMPP) wiring harness and controllers available for their crate engine kits.

The Devil is in the details with any LS conversion project.

A 13-pin 4L60 (non-ISS) controlled by a T42 TCM will work just fine, as long as the TCM calibration is one for a non-ISS 4L60. Likewise, the ECM calibration must be one that will communicate with the older T42 TCM calibration.

Your 2009 Silverado E38 ECM calibration would have been originally mated to a 17-pin 4L65 (ISS and internal Gear Position Switch). It may communicate with a T42 TCM setup for 15-pin 4L60 - but some tuning will be required to get everything sorted out.

Your 2009 Silverado E38 ECM calibration will not communicate with an older T42 TCM calibration setup for a 13-pin 4L60.

It comes down to matching the wiring to the components that you have, followed by matching the requisite ECM and TCM calibrations to the components that you have - and to each other.

This is not something that you can just slap together and expect to function correctly.