Since the clutch is new I would suspect it not the synthetic fluid.
Synthetic ATF should be fine to use, some say shifting is better, some say the same, some say it is worse, lol.
So it really is a users choice, but I don't see that as your problem at this point, could be, just saying the new clutch system is more likely the issue.
Ranger's hydraulic clutch system needs to be bleed a few times after installing.
Try pumping the clutch a few times.
Also try shifting into 3rd first and then into 1st.
When clutch disc is new it is thick and you need the full travel of the slave to prevent it from rubbing on flywheel and pressure plate with clutch pedal down.
You also need to use a Self-adjusting Pressure plate on this type of system because it doesn't have an external adjustment.
Regular pressure plate will work, but you will get what you describe, because pressure plate is not releasing enough on the new clutch disc so it is rubbing, this will go away as clutch disc rubs and gets thinner, then it won't rub anymore with clutch pedal in all the way
To get a transmission into 1st while stopped the clutch disc must come to a full stop, 0 RPMs.
The clutch disc is sandwiched between the flywheel and pressure plate that both always spin at engine RPM, on a cold engine the idle is about 1,200 RPMs, so flywheel/pressure plate are rotating at 1,200 RPMs, clutch disc was rotating at 1,200 RPMs in neutral, so when you push on the clutch pedal and then try to put trans into 1st the clutch disc must slow down to 0 RPMs before it will go into 1st.
That's where the synchro comes in, as you push stick towards 1st the synchro starts rubbing to slow down clutch disc(input shaft) to 0 RPMs so it matches the 0 RPMs of Output shaft(rear wheels).
Same can happen when trying to shift into Reverse, both have high gear ratios, 3rd has a lower ratio, it really shouldn't matter since 0 RPMs is what you need but seems to help slowing down the clutch disc.
I would first rebleed the system, see if you can get full slave travel.
Until then start engine IN 1st gear, and shift into 1st while still rolling up to the stop sign or light.