4l65e Issues

I was work on my tune when my 03 silverado ss stopped shifting into 3rd or 4th. Rebuilt the trans about 1k miles ago used all good parts and all new solenoids. After driving it a little off and on. When it gets up to temp. It wants to shift 1st 2and and stay there. If I hit the tow haul it will shift in to 3rd pulls fine no slip. Turn off tow haul it will shift into 4th and all good. If it ever down shifts into 2nd it will not upshift into 3rd or 4th.

No one??

Any codes? Maybe DTC P1870 for slipping?

Rick

No codes at all. Don't even try to shift I am hoping I can work on it this weekend.

does it work in manually?