[Snoopy49]

I’ve heard going into first is harder (it is for me) as they don’t have syncros in he first gear.


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Forward gears are synchronized and helical cut.
A reverse gear operates through a constant-mesh, fully synchronized system.

 

[Snoopy49]

It sounds like the clutch pedal is not being depressed far enough to disengage the clutch plates.
From what I understand the clutches in the pre 13 cars don't fully disengage until you get the clutch pedal almost to the floor.
The problem was "corrected on the 13-14 GT500's through the use of a different TOB and clutch master cylinder, thereby creating a new problem, clutch pedal not engaging until it is at the top of the stroke.

I would check the fluid level, bleed the clutch system and remove any air so you will get full stroke.