These control/alter the shift points on the AW4 4 spd auto trans. In 'comfort' the tranny will upshift sooner & softer(?) than in 'power'. In my 89 I really can't telll much of a difference between the two settings, but in the 88 (with fresh rebuild) I can. I leave the 88 in the 'power' mode.
I'm pretty sure they are an 87-90 (non-HO) thing and IIRC went away with the intro of the HO 4.0 in 91, but I am not clear on that. The earlier 4.0/AW4 XJs had a seperate tranny computer, and in the newer ones this function becamer integrated with the engine computer. I have heard that the new default setting is close to the old 'power' setting.