I have a Sprintex SC installed on my TJ 2006. It came with Hypertech max energy Tuner rebranded as 'sprintex'. Everytime I try to accelerate while shifting from 1st to second gear or second to third, I get this sudden hiccup / hesitation for a a second or two and then the power gradually kicks in. I havent yet monitored any of my AFR readings to see what exactly is happening. Few days ago, I thought of running open loop full time and see if I experience a difference. Since I dont have any access to a tuner other than the HPT nor do I have the expertise in programing things myself, I decided the simplest way to force open loop is by unplugging one of the upstream O2 sensors (bank 1 sensor 1 - the one which has its plug visible from top side of the engine / passenger side). The difference was night and day!! the jeep drove with so much instant power like had never experienced before. It felt like it had a lot of responsiveness, instant pull and the shifting between the gears has become so smooth with no sudden glitch in power like before.
I am really not sure what to derive from this, but it sure makes me want to drive my jeep with that O2 sensor never plugged in again!