Intermittantly misfires/stumbles at cruise, eventually goes to 1400RPM limp. Cycle key and all is well for a while.

Sets following codes in this order.
P1620 5v ref circuit 1 low voltage
P1120 Accel Pedal position sensor 1 low input.
P0335 Cant remember if range or circuit now.

Pedal and crank sensor have been replaced with new.
Found water in a pedal connector giving range codes, this has been resolved.
If crank sensor disconnected sets P0335 open cicuit, SVS MIL lights, same drivability symptoms.

TIS says P1620 The internal control unit reference voltage is less than 4.8v. (Short circuit to ground or circuit interruption)

TIS also identifies the Reference circuit as the 5v supply to crank & pedal. Supplied on pin 44 & 39.

I cannot find a short at present. Have gained good access to the two looms concerned and heaved them about whilst monitering for code status change with Tech 2.

Anyone experienced this before?
New ECU is £859+VAT, then there is the coding issue. Local dealer has sold two since 2008.

Have I missed something?