Though the OP did not ask...and I believe no one else even mentioned...

In manual mode the vehicle is gonna get worse fuel mileage.

That would be the big difference.

Most auto trans vehicles are designed to upshift early, boring, yet saves fuel.

These trannys were great in the snow country.

Go directly from L to R or vice versa, rock the car, to get out of stuck conditions.

Geezer memories...LOL

I have compared mpg. There is no difference when I shift manually for saving gas. I can also shift for performance driving, then all bets are off.

If OP wanted power, they would have bought a Mustang. They bought an 86, they already chose bliss.

serious question. Is is damaging to manually shift an automatic that doesn't have a "manual mode"? Every auto I've ever seen still has manual gear selections. Is it bad to use those to row through the gears or are they just made to hold the car in a certain gear?

Unless you shift to opposite direction gear or park while the vehicle is still moving, manual gear shifting is never a problem. Automatic transmission shifts perfectly every time since the shift is actually done by the transmission itself. Just engine/transmission wear can be a problem when you hold the gear at low and drive at very high rpm for extended periods, not mentioning the waste of gas.

Depends. Some would be fine and others would lead to disaster. Can't really give a yes or now answer.
Try shifting from D to L at about 50MPH with a 64 Chev two speed Powerglide tranny and watch the show as everything locks up as the engine screams (believe me).
Modern computer controlled trannies on the other hand would deal with it just fine.

nice argumenthttps://babang.xyz/assets/19/o.png

No replacement for the complacent?