With the engine and transmission warmed up (from driving it for a little while in L2 perhaps, you should stop on a level surface and with the engine running and foot on the brake put the transmission in each gear for a couple seconds, and put it in park and leave the engine running. Then with engine running check the dipstick for proper fill. If it is under full or over full, I suppose that could cause trouble.
The electric connection is just the kick down, and the truck will drive like normal without it. The only thing it does is when you are going down the road and press the gas pedal all the way to the floor, it will drop to the next lower gear and that will make the truck accelerate quickly. Some people might call it passing gear. For purposes of getting the truck going, you can just disconnect it. I think that is the orange wire, you can confirm, with key on but engine not running, when you floor the gas pedal do you get 12V on that orange wire that connects to the vertical prong on the transmission?
The other missing electric connector prong was only on some transmission/truck years, and it is for transmission controlled spark. You don't need that.
This is what my transmission connector looks like, with just the kickdown vertical prong. I have not connected it yet, but plan to.
