My dad's truck has 124xxx on it 454 4x4 and the speedo is bouncing all over and it won't stay in over drive...he has replaced 2 sensors 4 diffrent times and still nothing...speedo won't read right at all
1st check all the fuses, then use a voltage meter and check for 12v (key on) at the pink wire going into the transmission plug. Grab the harness and move it around, make sure it's not dropping voltage. If that's all good check the pcm ground. If it's not good, replace the pink wire from there to the fuse block, possibly up the column if it needs it.
12v @ pink wire "E" this is for 4L60E but should be the same for 4L80e
Ok I will show this to my dad I really hope that's all it is
It rubs through and shorts out, causes a lot of weird symptoms and usually throws the transmission in limp mode. Pretty common on s10s, I've heard of it on full size too.