Your truck most likely has a 95 amp alt, which should hold up just fine to the roof lights. How many watts are they? I am pretty sure it only takes around 40-50 amps for the truck to run, the remanding 50-30 amps is for things like headlights, power windows, 4x4 shift motor, wiper motor etc. So as long as you dont turn the lights on, run both power windows up and down, put the wipers on high, and put it into 4x4 over an over, you wont notice the extra amp draw.
My 130 amp alt holds up fine to 6 130w KC's, and 4 50w headlight/fogs, and 4 50w back up/puddle lights. When they are all on they draw about 70 amps @ 13 volts
My 1000w rms amp is enough to dim the lights and drop the system down to about 8 volts. When my subs hit peak power they draw around 75 amps.lol If I turned all the lights on and cranked up the stereo, I am sure I could fry my alt, but I have no reason to turn everything on at the same time. Now that doesnt mean I am not looking for a cheap 200 amp alt though.
Watts/Volts=Amps
-plumcrazy