If you didn't have an intercooler a short initial pull on a cold day after letting the truck reach its operating temp would probably yield similar numbers to an intercooled truck on the same day. But as you hold continued boost and do multiple pulls everything gets hotter, with no intercooler to bring the compressed air temps down, the engine and intake air as whole would continue to get hotter and you'd start to see reduced power. As long as the stock intercooler can consistently bring the temps back down to 10-30 degrees above ambient your IC is doing its job. On super hot days, if your intercooler isn't efficient enough it can become heat soaked and you'll have a power drop.
When users increase boost on stock turbos the air gets much hotter, sometimes it exceeds the stock ic efficiency and you will loose power even though you see more boost. Bigger turbos help to give you more volume per psi of boost and this helps keeps temps down too. Aftermarket IC Essentially gives you better efficiency at bringing compressed air back to ambient temps. I'm betting that the stock ic is just fine for stock turbo and turbo boost, and that an aftermarket ic with not other tunning would net you no hp. It might on a 120 degree day in stop and go traffic give you a slight advantage
