I have a 91 Toyota as well. Mine is 4×4 and I love it. Here’s the facts. Downshifting may not harm your transmission, but it does engage your clutch. The clutch plate does wear out over time, and the best way is to only downshift when necessary, like cornering or to avoid a situation. Otherwise, leave it in whatever gear you are in as you come to a stop. Keep your foot off the clutch. Pull it out of gear and put it in neutral just before the engine lugs to die. Pulling it out of gear without using the clutch does NOT harmthe transmission as long as you ar enot forcing it. While sitting at the stoplight, stop sign, or at any sort of stop, do NOT engage the clutch until you are getting ready to go. (this is the number one error people with a standard transmission make, of sitting still and holding down the clutch with the vehicle in gear). Just sit in neutral with your foot firmly on the brake. Here’s why.
The clutch plate wears out with use. Sitting at a light with your vehicle in gear and your foot holding the clutch down creates unnecessary wear on that plate. You are burning up the clutch while you are not moving. It is not necessary, and when it comes time to replace that clutch, it is going to cost you a fortune. Brakes are cheaper than clutches. My mechanic told me this. He has a 1996 Chevy S-10, standard transmission, and has never replaced the clutch. I just paid for new brake calipers on my Toyota, and it was expensive, but not the $1600 it would be to replace my clutch.
I also used to drive an 8 ton commercial vehicle (Haz Mat with air brakes) and that was how I was taught, to not use the clutch unless absolutely necessary.