I hope there's a solution, cuz I won't drive GTL anymore like this... 
Any help?

Go on GT, you dont need GTL anyways. Time to get hooked on a decent Sim with very good netcode
That remark will certainly help him a lot... :nope: (you could also say: don't play race sims, that certainly helps too...)
BTW: if you don't like a game, don't repeat it on every occasion, it gets annoying.
ON TOPIC:
I think you should check out the PLR file, I had a lot of troubles in the past with bad feeling on steering, brakes, throttle with various sims like rFactor (still not as it should be), GTL and RACE
I think the most important if you got serious trouble are these settings (a part of the PLR)
Axis [00, 00] Dead Zone="0.00000" // Controller 1 X
Axis [00, 00] Sensitivity="0.50000"
Axis [00, 00] Center="0.50000" // 0.0=min, 0.5=center, 1.0=max (use to correct centering or split-axis issues)
Axis [00, 01] Dead Zone="0.00000" // Controller 1 Y
Axis [00, 01] Sensitivity="0.50000"
Axis [00, 01] Center="1.00000"
Axis [00, 02] Dead Zone="0.00000" // Controller 1 Z
Axis [00, 02] Sensitivity="0.50000"
Axis [00, 02] Center="0.50000"
Axis [00, 03] Dead Zone="0.00000" // Controller 1 RX
Axis [00, 03] Sensitivity="0.50000"
Axis [00, 03] Center="0.50000"
Axis [00, 04] Dead Zone="0.00000" // Controller 1 RY
Axis [00, 04] Sensitivity="0.50000"
Axis [00, 04] Center="0.50000"
Axis [00, 05] Dead Zone="0.00000" // Controller 1 RZ
Axis [00, 05] Sensitivity="0.50000"
Axis [00, 05] Center="1.00000"Axis [00, 06] Dead Zone="0.00000" // Controller 1 S0
Axis [00, 06] Sensitivity="0.50000"
Axis [00, 06] Center="0.50000"
Axis [00, 07] Dead Zone="0.00000" // Controller 1 S1
Axis [00, 07] Sensitivity="0.50000"
Axis [00, 07] Center="1.00000"
The lines in red are the ones of the brake pedal (1 RZ axis), but it could be related to bad settings of the throttle (1 Y) too (others are less likely)
Info:
1 S1 = clutch pedal
1 X = wheel