Slow in reverse, not much power

Several oil brands have "high milage" oil for vehicles with high miles. I would go with a 10W/30 oil.

Did the mechanic adjust the fuel injector if you have noticed ?

earth cable from body to engine and battery to chassis ,clean the connections and fit an additional cable ,also clean and grease the battery terminal

Do you have an owners manual?

Check the bulbs to see if they're good (rare that both bulbs go at same time). If they're good, check to see if there's power to your sockets.
Under your car on the side of your transmission will be your reverse switch. It will have several wires coming out of it. Most likely the switch has died.

Rebuilding the transmission. That's quite a few miles on your transmission and the seals are finally letting go.

Sorry to be the bearer of bad (and expensive) news,
matt

Since the fluid level is okay, I think your gonna need a rebuilt transmission. Tow it to a good transmission shop.

If you have checked Power/Ground, and alls good look toward the Multi-Function Sw. (turn sig.sw) this is where everything get distributed at...as for your power loss when shifting, is it column/floor shifter ???? need to know....

This is a front wheel drive vehicle and has no power-train components in the rear of the car. The noise coming from the back is not related to your transmission. I would highly reccommend going to a ford dealership as these are typically trust-worthy and always use OEM parts. I also have an 03 sable with 101k miles it has always been reliable and has original transmission. It is possible something else is hard ****.

Hello and thanks for using FixYa!, the problem with your sable is that the transmission range sensor needs to be replaced, back in 1996 and 1997, the circuitry internal to the sensor caused an interference with several other systems in the car, including the radio, power steering and power windows. Have the sensor replaced and it will need to be adjusted, so it is best done by a ford dealer who would have the proper alignment tool.