I have 1988 V6 2.9 Ranger. Having problem with gas gauge. We have already replaced the pump and sending unit. It will regester full until 1/2 of tank then on the gauge go to empty.

The gauge itself may have failed. Sorry I don't have the specs available at home but you can put a variable resistor in place of the fuel sending unit and causr the guage to rise and fall - I just don't know the specific resistances to use. The gauge as well as the IVR (Instrument Voltage Regulator) can cause this. My old E-100 would do the same. I just watched the odometer and whenever I got around 200 miles, I just filled her up again (like an old motorcycle)

The varialbe resistor or IVR, is this a BIG issue to install?

It's attached to the back of the instrument cluster on the printed circuit board. Set some time aside and be patient because plastic parts that old are easy to break. It looks like a little rectangular can.

Check your float when you pull your fuel pump out the gas tank your float might have a crack in it like mine was.This will cause it to read empty.Shake the float and you will hear gas moving around inside