Idle rough loses power when hot

[Rici13]

Hello everyone

I have a 1994 Silverado K1500 with a 4.3L, 120 K, the idle speed jumps up and down all the time, it varies around 300 to 500 rpm. When I start the car the power seems alright but as soon as the engine reaches operating temperature the cars loses power, I can hear a constant pop in the exaust and the idle goes even more jumpy. I have good sparks, cables, cap distr, new O2 sensor. Timing is set at 5 deg BTDC.

If someone could help me figuring this out, could it be some sensors?
Thanks a lot everyone.