480le problems

[chadritchey1983]

i have a 2007 1500hd with a 4l80e that started overheated and not shifting ive replaced the lines the cooler put in a salvage transmission rebuilt the original had a rebuilt put and even had a brand new one installed and not one has worked they all have started overheating shortly after they are ran what do i need to do to fix this 

[davester]

So, three transmissions, at a cost of $3k or so + labor,  What kind of diagnosis steps did you and/or your mechanic take to figure out what could be going wrong?