Delaminating clear, what to do

[racin69z]

I bought a truck that has paint that I am guessing is about 5 years old. The clear on the top of the bedsides is delaminating from the base. Everywhere else seems to be ok. I am wanting to know if I need to sand all the clear off the whole truck, or just sand what is loose off and scuff the rest prior to priming and blocking.

Thanks
Lynn