I need help with my truck overheating

I would put it on a scanner and drive it under a good load to recreate the issue. Could be something like the fuel leaning out under load (this can cause the cat to heat up and melt or break apart). Plus the scan would tell you why it's leaning out, bad sensor, etc. It could be a quite a few things really. Spend a little money at a GOOD diagnostic shop and get it fixed without having to change anymore unnecessary parts. Any codes stored?