2004 ford f150 5.4 not running during the day.

2004 Ford f150 5.4l v8 Latriat
187k
timing chain, oil pump, transmission and some exhaust work done.

My dads truck has some problems. It runs for few minutes then starts struggling to go then just turns off. Specially during hot day it runs for 20 min tops then starts struggling. Loss of power then turns off. So we had to pull over let it cool down for few minutes then go. And repeat this till we got home. He said it runs better at night when its cooler. He just changed oil pump and transmission. So what can be the problem? Cat converter?

Thanks.