1996 Chevrolet Tahoe 5.7

got the tahoe last week, which had a "transmission" problem which i fixed by replacing the ignition switch/harness. than another problem arose. it would just stall out of the blue while driving. it doesnt struggle to stay on it just dies. there are no dash lights at all, guages don't work, turning the key off and back on again still doesnt work. after about 20-30 seconds, the lights will come back on, and the alarm siren will go off. when it starts back up everything is reset. i have to re-set my clock and radio presets and there is no check engine light on. happend during rush hour during a long drive, and also happend after a cold start...

i have not had the vehicle long enough to know if this problem has happend before the switch change...