93 4runner tranny problem

Had a similar problem in my old commodore. While the above solution will fix it the problem may be something as simple as the bands in the gearbox are loose. In an auto box this is what holds it in gear and if they are loose this will cause the slippage. Grab yourself a good workshop manual, this should have in it how to do it. It's quite a simple job and shouldn't take you more than half hour.

Wish I had an answer for you...
I noticed my problem not in 1st gear but in OD or 3rd... I could see
the RPM's increase about 500 rpm (and actual speed staying the same)
when climbing small hills or even with stepping on the gas for passing
on simple in-town driving.

I had my 93 3L 4Runner tranny and torque converter rebuild last fall
(had 165K)... spent a little over $3K. What a difference! I get all
kinds of shifts up and down that I never had since I got it 2nd hand
several years ago.

Good luck and stay away from chain store tranny shops.
Dave-in-Denver