I am using tinyg with vcarve and have had great success. But today I have attempt to send large code (using universal Gcode sender) of about 275,000 lines. It starts to cut fine but about 120,000 lines into the code it slows down to about 2 mm ever 5 minutes. I think it would finish but never found out as after 1.5 hours of this I aborted the operation. This model has great and fine detail in a thanksgiving wreath.
I send another gcode file of about 100,000 lines which was successful.
Using UGS does not have a line limit/size of Gcode files AFAIK.
There are some issues with Chilipeppr, which uses a different and much more aggressive buffer management strategy.
Just how 'fine' is your fine detail? Are the move commands in that area of Gcode moves that tinyG should make? To estimate, calculate the move made by each step pulse in X, Y and Z. A step pulse would be a microstep at your microstep settings. So if your steppers are 1.8 deg (200 steps per rev) and microsteps = 8, tinyG will issue 1600 steps per revolution.
Divide distance moved each rev by 1600 to determine the minimum move.
You could just try to cut your microstep setting in half (say 8 to 4) and rerun you job in air to see if it still stalls.
Sounds like a real long run time job, maybe edit your Gcode file to just send the fine detail.