My headlights on my gmc jimmy are not working. the dash indicates that the high beams are on but indeed they are not and i cannot turn this off. sometimes the lights flicker on but then go out right away. any suggestions?

The usual cause is a bad ground.
Check the ground with a test lamp.

Check the earth connection, sounds like it has lost the earth on the off side and both elements of the bulb are coming on together and halving the power ( causing bad elluimination)

headlights control by headlamp driver module relay to the BCM and the light sensor on dash next to the winshield defrost vents.headlights also control by high beam relay.

There is a headlight relay in the engine compartment fuse box, but its after the headlight switch and before the dimmer switch, so it powers both high and low beam circuits.
I would check the dimmer switch.

go to an accredited auto electrician for electrical work
it may be a switch problem but I think that there is no power to the light relays ( switch or fuses)
if that model has a light control module , it could be that

COULD BE DIMMMER SWITCH .DRL RELAY LOCATED IN FUSE RELAY BOX UNDER THE HOOD IN ENGINE COMPARTMENT.

You need a new headlight dimmer switch located on the steering column between the dash and the firewall

My first guess would be the combination/multifunction switch on the column (turn signal arm). Controls all of your problem areas.

Check for 40 amp fuse in vehicle but most likely under hood.

just try this. I had the same problem here a while back. try clicking on the high beam lever. mine went bad and was stuck in between high and low beam and would not come unstuck. and it caused the headlights not to work...