I have an almost identical station: IC-718, one end fed ant, one fan dipole, Signalink USB, and LDG autotuner. Mine does not drop power when using digital modes. I have not noticed any unusual heating.

But, I can only get up to 50 watts with digital modes (it's a 100w rig), then the power stops going up with increases in the TX audio level. At 50W, the ALC starts to rise from zero. Putting in JP3 in the Signalink for increased TX audio did not make a difference.

Mike KA2JAI