hmmmmmmmmmmmmm, if it wasn't the ivr a new one should have given u the same results right???????? my oil reads just above the o in "normal" when starting then lowers to between n and o when warm. since the other gages seem to not be erratic at the moment the only thing i can think is... was it a motorcraft part?........

the ivr is the same whether u have dual tanks or not. the ground for the fuel senders is a black wire connected to a clip with 2 or 3 the other wires under the dash, to the left of the steering colum on something known as the "y" brace. its always a bit loose and might have some electric grease on it, see if it's very loose and needs tightening.

i have an electical manual from ford for my 87 it has some other troubleshooting steps
if u have a tester... but when multiple gauges are erratic it's usually the ivr.

let me know if its a motorcraft ivr. if u have the part number i can check it with a friend that works at ford.

good luck. glad the cluster came off for u.