first check a wire loom about an inch thick that rests on a stud popping out of the engine block. this stud can wear the loom and cause shorts. Inspect wiring closely.
these wires are towards the back of the motor near the firewall.
check if any o2 sensors have shorted out by wires touching the exhaust
if good then,
you need 2 upstream o2 sensors and 1 downstream sensor
p0051 &p0031 are upstream
p0136 is down
and check ecu for rust n stuff(wires)
4.0, 5sp, bfg33's, 3 1/2 lift