been toying with the idea of just using 3rd and 4th gear....
 

might be a little harder accelerating uphill from a stop but would there be anything else I would need to worry about? I have a 4t60e tranny. Figured I could just use a toggle switch to turn on 4th and use a lockup switch. or an I just wasting my time and would be better off with JUST a lockup switch.

With an auto, that won't help mpg much. You'll be slipping the torque converter a lot to get moving, so you'd also need a BIG tranny cooler to avoid cooking things.

My dad never got used to 4-speeds. He called 1st gear "creeper" and only used it occasionally. There might be some advantage to skipping 1st if you are not in a hurry, but I'd definitely use 2nd.

The 2 speed powerglide is touted as one of the most efficient transmissions there is, for power transfer.

That said, without altering the transmission, I'd look at 2nd and 4th with a lockup after 20 MPH.

Shift into 4th while still locked at about 35-40 MPH.

i was always impressed i could start from 2nd and easily shift without the clutch on my 1985.5 lynx.

passengers would spaz-out and say "that's horrible for the car". lol.
i can't be sure i would;ve achieved 70% success on starting from 3rd.

Lost the shift linkage in my Topaz years back, it fell right away from the transmission while I was going from 5th into neutral.

I had to move the car, so I slipped the clutch in enough to get the car moving, then just let it go and gave it really light throttle. I had no problem getting back to 60 MPH without shifting gears, it just took longer than usual.

When I got home, I bent a good sized nail, fed it through the hole, and bent the other end too. Drove it like that for another couple months back and forth to work every day.