We have a new to us 1991 Toyota SR5 V6 4x4. It has an Automatic transmission, which i have not owned many of (I am stick guy). The trany shifts very smooth, however does something strange to me. When you floor it (in 2nd and up) the RPM's go up to 4,000~4,200 RPM's, then drop down to 3,600~3,800 RPM's, then climbs the rest of the way past 4,000 RPM's all the way up to redline. It is smooth, the truck keeps pulling when it does this, and the speeds do not drop. Is this normal? Is there like 1/2 gears in the trany? Torque converter locking up? Slippage? Is this something to worry about???
Here is a pic of the Truck:

 

Bingo.

 

Is this a good or bad thing?

 

It's normal from what I can tell from your description. Next time you are at freeway speed, push the gas down until it downshifts into 3rd, hold it there and take note of the rpm's. Now turn overdrive off via the button on your shifter. The rpm's will drop by about 500. If this is the same feeling you are describing above, it is completely normal. And now you've just learned a little trick to getting more out of 3rd gear.

 

Yup it is the same! Thank you very much!

 

Another little trick: to get the t-coverter to unlock when you want it to, tap the brake with your left foot while you are on the gas.