2000GMC sanoma flashing lights

while driving at 35 to 40 when i let off of the gas the lights flash just for a second, i have tried this several times at night on the way to work and i will keep a constant speed then let off of the gas and the lights flash, the dealer said they had a shop note on it and i had my mechanic make the repair it was adding a part to the altanator but now its doing it again so i need some advise as to the next step to solve this problem, any help?

“Shop note?” What’s a shop note?

Are you sure your mechanic did everything the dealer would nave done?

I’m not normally a proponent of dealers, but sometimes they know best.

I agree with MC and I might suggest you check BOTH ends of each battery cable, making sure the contacts are clean and tight. You might want to try turning the lights on, engine not running and see if the lights react when you move the cables around. They can get internal problems.