Hello, I just started driving my swap, its a 5.3 + 4l80e (2002 model from a chevy 1500) it has a HD2 shift kit.
I will upload tune and scan soon. For now, just in case this is a simple common issue, pretty much as soon as I start moving from a stop, it shifts into 2nd right away. IF I put it into 1st manually I will hold 1st. It will also downshift 1st from 2nd manually.
Once it gets up in speed a little, it goes 2->3, and then right away kicks back and forth between 2 and 3. At first this seemed like a tire-speed + rear gear issue so I corrected my speedo for the rear gear and tire size, but it still happens exactly like before. In fact nothing seems to have changed even though I adjusted all my shift points, it still shifts when it wants to.
Once I get enough speed, it sticks to 3rd finally. So it must be in the computer telling it to up and down shift. Then it goes to 4th also just fine.
for now, any suggestions, <3 thank you. Otherwise, I will continue to diagnose and examine the issue till I figure it out!