Forget GIMP, forget Photoshop. Get Autostitch, it’s what a lot of prosumers use, including myself. It may look like a dorky, unfinished, unpolished piece of software because of the site design but trust me, this software performs hands down far better than most others.
After you’ve stitched your panorama, you can post process in your other application to your heart’s desire.
It used to be free, but I see it’s not now. Check around on their links for your best pricing. Serif is usually fairly competitive. There is a demo but it may have limited capability, I haven’t tried it, but you should check it out.