Hi, Scotty!

I have a 2001 V6 auto Mustang. Since the day I bought it I’ve had a weird acceleration hesitation issue. The car will gradually accelerate without issue, but when merging on a highway or needing to pickup speed quickly it hesitates. It is much worse when under additional load from having my A/C running. I’ve replaced: Plugs, coil pack, plug wires, intake filter and fuel filter. I’ve also cleaned the MAF, throttle body, and IAC. It almost feels like a misfire but I’ve never had a code for that, only an Evap leak. My searching leads me to believe that I have a vacuum issue or fuel pump, any ideas?

I'd change the fuel pump first, you didn't mention changing that. Number one on that, number two would be dirty fuel injectors, try this for that: https://www.youtube.com/watch?v=bKGI9N_yWd0