Yes, I do have another idea on your perplexing problem. The TV valve is notorious for sticking, especially after going to full throttle, whether the engine is running or not.

When the TV valve sticks in a high throttle position, governor pressure must go to maximum for a 1-2 shift to occur. When TV pressure is at maximum, it also makes main line pressure in the transmission elevated, too. You can verify this by simply going from Neutral-to-Drive or shifting Neutral-to-Reverse and you will notice the engagement is harsher than normal. The main line oil pressure tap on this transmission is on the driver's side of the transmission, slightly above and to the rear of where the shift shaft goes into the transmission. 7/16" wrench w/1/8" NPT. If you put a pressure gauge on it, normal is 65 psi @ 1000 rpm in Drive, but if the TV valve is stuck, it will be much higher than that.

A "trick" to get it unstuck w/o pulling the pan is to "flash the throttle". With the engine idling in Neutral, very quickly slam the throttle to the floor and let off. Do this so quickly the engine doesn't have enough time to really rev up. Do this both in Neutral and Park several times, but always finish it up in Neutral several times.

This throttle flashing procedure will get the TV valve unstuck over 50% of the time unless there's excessive debris in the fluid. TransGo makes a valve body kit that has a patented "anti-stick" TV valve that you might want to consider if and when you ever pull the valve body again.

FWIW, a sticking or binding TV cable will give you the same symptoms as a sticking TV valve.

Good luck...

Larry Bloodworth
Technical Information Specialist/Technician
Tanner Transmissions
Draper, Utah, USA