I'm battling some issues right now trying to pinpoint the problem. I just bought new trans cooler lines, plan on changing them this weekend. There is a check valve on supply line to cooler that people have said fails blocking flow through cooler. I took mine off and cleaned it but I don't trust it or the lines at this point. I've been monitoring my trans temp with scanner and with no payload I'm reaching 230*+ at times and others running around 180-210* which with a 195* stat is normal. When I bought the truck back it didnt shift and had a code for gov pressure. I replaced solenoid and sensor, as well as I did fluid/filter, adjusted bands. It's been good until this past year.
Did your trans fail or are you taking preventative measures?