I had this exact same problem when i first bout my '04 Titan in '08. When i was driving down the road, i'd press the brake and the brake light would come on and the pedal would pulsate to the floor and the front tires would lock up (abs engaging). Cut the truck off as u did and it goes away for awhile. Same exact issue. I took mine to a Nissan dealer and they reprogrammed the abs and it fixed it for two weeks before it did it again. Then they kept it for two weeks until they diagnosed it as the ABS Control Module and so they replaced that ($1400). Got the truck back and a week later it did the same thing. Well i took it back and then they diagnosed it as a brake booster. So they replaced that, after a two week backorder, and i haven't had a problem since. In my experience, it is going to be the brake booster on the truck. How or why i do not know but that's what they replaced on mine after about a month and a half of being without the truck.