Need advice - trans issues

[GroundControl1]

Recently got one of my dream vehicles, traded my 2020 Tacoma for a 1988 FJ62... it's almost perfect.
If the fluids are cold in the transmission it does not like to shift into 3rd gear, when it does shift the RPMs spike right before the shift. After the fluids warm up (around a minute or two of driving) it shifts perfectly fine with no issues at all.
Checked the fluids, the trans fluid was reddish brown, did not smell burnt, had no metallic particles, but was slightly overfilled. Took out around 6oz of trans fluid to get it back to where it needs to be, but that hasn't not changed the shifting issue.

Want to get some advice from guys that have dealt with similar issues or just knowledgable people with transmissions that can point me in the right direction.

I do have a spare A440F transmission if I need to swap parts. I've considered getting the spare transmission bench tested and just swapping it if I can't resolve the issue in the current one.

 

[BurntToast]

Check if your TV cable is getting stuck, do a Rodney Flush, or the party trick?

Real solution is to put the manual in it.

"The Rodney Flush"
Here is a full set of instructions to do an Automatic Transmission full flush and oil flow test all at the same time. I have done it different ways but the best way I have set out below:
*Remove the front drive shaft. *Undo the rear cooler line from the rear transmission union. *Slid a rubber hose over the cooler line and direct it into a bucket. *Either drain the transmission using the drain plug or service the transmission. *Refill the transmission with 1 and a half gallons of transmission oil (Synthetic Recommended). *Start the car in park and hold it at 2000Rpm for 60 seconds and turn off. *Measure the oil in the bucket to find out transmission flow. *Add another gallon into transmission. (Engine Off) *Restart car and let it just idle until the oil changes colour to a nice clean oil, you will need to ad some oil as you are doing this to keep it flowing. Then shut engine off. *Refit rear cooler line. *Refit front shaft. *Restart car and top up the transmission to correct level.