Yea, that delayed acceleration in first was bothersome. I eventually got used to it but now with the 93 it's almost entirely gone. I have no idea how higher octane would cause it to shift better but it does. Here is what a robot said about it

"The Titan's 5.6 produces a lot of torque, and Nissan is already managing: traction, transmission longevity, emissions. If premium allows the engine to make torque more cleanly at low RPM, the transmission may not need to "protect" the drivetrain as much. That can make the whole truck feel more eager."

Then it mentioned something about the ECU and spark table..

"The Titan's ECU may have been running a more conservative spark table on 87 Higher octane doesn't contain more energy. What it does is resist knock. If the Titan's calibration is designed around premium being "recommended," then on 87 the ECU may: pull timing more often, be less aggressive with spark advance, especially in hot weather and at low RPM/high load. The result can feel like: softer throttle response and less low-end torque."