V8 discovery 2

Hi all.
I have a discovery 2 v8 auto.

I have recently bought it and have changed all oils.
I find that when I’m driving it it seems to struggle going up through the gears. It seems to need to be reved up high to change the gears and once in the next gear it seems to jump down the gears. Also sometimes when driving I can’t get over 3000 rpm. I’m lost on what is the issue.
Help.
Thanks

Hi. Run a stall test on it maybe the problem is reduced to one area... btw how was the oil's colour which came out from the gearbox ?