I assume your friend is probably talking about "limp mode" which is a default state that your truck would enter if it had a critical fault from unplugged sensor or sensor failure (not all sensors cause this condition). Simply plugging in an OBD2 hardware interface won't cause this problem. Of course, if the hardware or software isn't engineered well, it could create a fault condition, putting the vehicle into Limp.
Limp mode puts usually puts the ignition advance into a retarded condition which limits horsepower.
Now, if your interface box is pulling lots of parameters from the vehicle while the ECU is trying to manage the ignition / fuel / etc. systems, there is always the possibility that it can't "keep up" and have a misfire condition (intermittant). Similar to a video glitch running a new game software on an old PC with slow mhz.