Thanks for all the help.
Time for some measures:
My Supply outputs 12.81V
When pwm output is at 100% dutycycle,
I measure 3.62V directly on the GPIO pin, after the 1K resistor its 3.31V, and after the 1,5K its 3,15V
The mosfet gives me 12.31V on the ledstrip with the 1K or 1,5K (doesn't make a difference) and it's very bright, i don't see any difference between direct supply and mosfet supply, so that works perfectly.
Unfortunatly it looks like i can't measure any current between the GPIO and MOSfet, but i think that's because i still use the same cheap multimeter as since i was 11 haha (28 now btw.. so lots of years of abuse
), so i think its time for a replacement.
Also i discovered that the leds get brighter with the 1K/1,5K resistor instead of the diode, (resistor drops only 0.30v/0,45v while the diode dropped 0.7v)
so i should remove the diodes and put the 1K or 1,5K in place?
Could it be smart to take an even higher value? the highest possible resistor before it would drop under 12V?