Place all ingredients into pressure cooker. Place on medium heat with the weight off the cover. When the pressure cooker starts to jet steam time for five minutes then put the weight on at 15 pounds. When the weight starts jiggling set the timer for 45 minutes & adjust the heat so the weight jiggles every few seconds. When the timer goes off remove the pressure cooker from the heat & let sit for 10 -20 minutes for the pressure to reduce. Remove the weight. When the pressure cooker stops venting steam, remove the cover & let the roast cool enough so you can shred the meat. Replace the meat into the pan(you may want to add more picante sauce) & place over medium heat to rewarm. Serve in flour tortillas with the usual ingred's for tacos.