Transmission not working properly/slipping?

Hi, I need help.

I have the vehicle listed above with 290,000 kms on it v6 4.0 Canadian spec
The engine is all good it just leaks oil through the oil pan.
And there's no code.
But sometimes after a long drive in city for like 30 minutes the gear goes to neutral it slips and does not accelerate a bit I put it in P and than to D still the same. Then I change the gear to D1 (low1 in automatic) and than it works perfectly fine without slippage and then works fine.
It also happens when I have load in my car it seems like transmission is struggling at 60 MPH on an uphill it seems like it downshifts and upshifts with a jerk sound and a little jerk. It seems like it happens when the car is on load like accelerate on a tight corner, or an uphill

It also produces a jerk sound when shifting to D from P or reverse. I had new transmission fluid 2 years back

It often goes to neutral and than sometimes it also slips a lot like 1,500 RPMs I am accelerating with little slippage but after 1,500 the revs goes up the car doesn't move at all and sometimes it doesn't move at all even at 1,000 RPMs or 1,500 RPMs or 4,000 RPMs.