Typical no-shift chevy
 

I have an 08 silverado 4.3, 2wd that is having erratic shifting issues. Some days it shifts perfect then other days, it will not shift out of first and speedo doesnt work. This usually happens after a take-off from a complete stop. Pull over to side of road and pull it down into first, then shift manually and it will shift. Also speedo needle bounces between 0 and 10 mph when at a dead stop. Have already changed vss with oem part and this fixed it for a couple of days, now it is doing it again. As i said, its erratic and doesnt happen all the time. It is the 4l60e trans. The cel has never came on at all through all this. Also, the "transmission hot, idle engine" message comes up all the time. I can push the button to read transmission temp and it jumps like 140;180;235;170;300;150,210,240. Just like that and about that quickly. Trans fluid is not burnt smelling and transmission never seems hot. I am about ready to junk it!!!!! Anyone have any ideas? Like I said, check engine light has never came on through any of this!

Typical no-shift Chevy
 

And to add to the problem, now the abs light is on and truck is doing it all the time now. Still no cel light on. I guess no one here has any ideas.

This is a tough one. Seems electrical. I'd make sure the harness that goes into the trans is good and tight. Checked for chafed wires.

Check the tcm for codes. This will require a code reader with access to Chevy specific data. The hypertough ht200 from Walmart works great for this. Its a rebranded autel ap200 for only $50.

Vehicle speed sensor would be my take on your issue.