Suzuki Vitara Alternator??

[slayer921]

I have a suzuki vitara that has recently developed a fault where if i turn the lights or the heater on, it revs up to about 3000 rpm!! Is this an alternator fault?? At night its like a cruise control at 35mph in 5th!! Battery has been checked and seems fine!! Wot could it be???

Thanks for you responses in advance!! Tom