RPM's drop as if it were going to turn off

Greetings, I have a problem with my truck. In low function, with its correct rpm, when running, the rpm drops as if it were going to turn off, I have to accelerate it hard (over 6,000 rpm) and in turn creates an explosion counter, and stabilizes.

I changed:

Idle control valve
Knock sensor
EGR valve
Electronic Spark Control

I checked the vacuum lines and found none broken.
The timing is correct.

And I continue with the problem.
Someone could know what the problem would be.