In desperate need of ideas!!!!!

[J3mom]

I have a 1998 Subaru Legacy Outback Wagon:2.5liter with 275k miles. A month ago I took the car in for new brakes, oil change, and check the check engine light code. The codes that came up were P1083 and P0420. The shop checked the catalytic converters and they said they were running good. I left the shop and about 2 miles down the road I was stopped at a red light. The light turned green and I pressed the accelerator and nothing happened. The car had died. It started right up and then died 2 more times. Took it back to the shop and they drove it around, nothing happened. Two days later, it died at 4 different stoplights but always started right up. Shop then had it for 3 days and not once did it die. My husband replaced the fuel pump relay, fuel filter and fuel pump. Cleaned the MAF, and the IACV. Car continues to spontaneously die at lights and sometimes while turning. It also cuts out and the tach drops and you can feel the car try to die. We've been to 3 different shops and no one can figure it out. Any ideas would be truly appreciated. It's becoming a safety concern when I have my kids in the car and never know when it might die. Thank you.