'91 Caravan Loses Power (Code 21 & 52)

I have a '91 caravan (3.3L) that runs great except for a problem that occurs with power loss at highway speeds +60mph. Vehicle will run very smoothly, then may lose power without warning. It seems as though it is starving for fuel. New fuel pump/filter etc. Mechanics are unable to recreate the problem and diagnose. Computer trouble codes 21 & 52 are present. Problem seems to occur while vehicle changes speeds and perhaps more frequently with cruise on. Does this sound like an O2 sensor issue or maybe fuel inj.?