Bought a 04 Volvo shifting question. Automatic.

Auction buy. 2004 Volvo D12 12 speed Meritor automatic transmission. *i think* price was dang good. Bunch of minor fixes, batteries, yes high mikes 960,000. But I am figuring 3000 miles a year.
Got it legal but the automatic transmission confuses me. *only 250 miles so far*.
On start CL *or CH* and AL flash. After few minutes they go off. Starts in 3. Which normally is fine. But today going across worked field to line up under auger. It was fine in 3rd. But it decided to shift to 5th. Fine on tar. But field? By time it shifted twice I was stopped, tires just spin. Backing up constant worked great. If it had stayed in 3 no issue as empty. It’s supposed to have manual option. How do I access it? Any YouTube have control on steering wheel. Mine is control ahead of hip. Brake forward goes into 3. Right button is N. So Push function button *left button* pull back, pause 2 seconds? in R.
Anyone know how to get manual shifting? If not how to temporarily lock it in 3rd?
O am impressed by it. 4 loads. *ok overloads* of corn. Last two barely over 80k runs smooth. Motor electric fan started today scared me for half a second. it wants to RUN loaded. But from stop. It does this dang double shift. 3,5,6,8, before I even complete a left turn. So REALLY slow left hand turns. As rural area not a big deal. But if I could manually button shift imo it would be much better.
I have driven 10, 13, 18 speed manuals decades back. But left leg injury even shifting few times is uncomfortable.

 

Sadly I have not figured out how to message here.

 

Thanks I will figure out the IM method here. . Still shocked I bought such a high milage truck. But so far 200 miles of 30 mi of 50 mile round trips. I think every minor issue me not working with truck. Mostly transmission. Maybe it takes 3 stop/start to adjust to empty weight, or full? It seems to jump gears just as I start up a hill. She does not love going 55. She wants to go over 60. But as farm use. Its longest drive is likely to be 30 miles without stopping/turning. I never minded crank opening traps. But dang are they nice having power ones.
The gear skipping on turns from stop. It hits no power to tires, feel it shift, almost start of power to wheels, then nope, pause shift, then finally power to wheels but lugging.

 

I pulled onto a dirt farm field. Going great in 3rd, empty. But it decided to jump to 5th. Double pause for dang near dead stop, then tire spin. Tried a couple, gave up, backed it 200 yards in RL smooth as can be.
It actually went into 2 yesterday. Fully loaded, starting up slight slope. I think truck did it? Maybe I had something changed? Jake setting? Not a place I could play with it. Honestly it’s working great. I just am not meshing with it. Not understanding how to adapt it for situations. Left turn, across 2 lanes +65 mph to turn left on 2 lanes going +65 mph with 20’ between roads. 2 LONG pauses of no power as it jumps 3 to 5 then immediately 5 to 7.
IMO if you always skip gears. Maybe 5 should be geared 4.5? 7 should be geared 6? Make it a 10 speed? For my uses it’s great. Short trips. My left knee shattered 95, replaced 2014. Does not bend much. So manual while I have driven. Takes body movement to start out. I am planning maybe 3000 miles a summer.