99nbs 5.3/4l60 to 4l80e trans swap.

[geoffcalii]

I have a 99 1500 2wd. It's a 5.3 4l60. Long story short I pulled the 4l60 after it went out and bout a built 4l80e. It's in now. Have the nelson performance 99-07 connection harness. I know I need to get the ecm programed still but I was told it would still have first and second gear until then. When pulling it out of the garage it doesn't seem to be in first gear. Almost like second or third. I think the 4l80 core came from an 02. Any help would be appreciated. Now I'm hearing 99-02 trucks have a different pinout. I'm can't find a definite answer.