Auto not gearing up/revving. Sluggish performance.

Hi All.

First time poster 'ere.

My 96' VS Statesman (auto) is having some sort(s) of transmission problems.
Whenever I put my foot down in an attempt to get acceleration, the car just sits in the same gear and the taco hardly rises at all.

Because it is not downing or upping gears properly the car has became quite sluggish. A good way of describing it would be it's like driving a manual car in 5th gear around the city streets in traffic!

If I drive putting it into gears 1, 2 & 3 respectively it seems to rev out properly and I get the proper power.

I thought it may be the transmission fluids - so I checked this. It turns out the Transmission fluid was low / borderline empty. So I put approx 2 litres into it (it properly needs more so I will put more in tonight). Also the Oil was pretty much empty (so i put a couple of litres in that also & plan on putting more in tonight).

I should point out i have recently had a 2nd hand motor put in which had done 140,000KM and have had a reco transmission put in approx 1 year ago.
I have changed the oil, leads, spark plugs recently, but I havn't flushed the transmission fluids for a while.

Any Ideas what this might be please?

Thanks in advance.

 

Thanks for the prompt replies guys.
If I was to try completely filling my transmission fluid to the brim, do you know roughly how much it'll take? I just want to make sure i don't under/over fill it. Im crossing my fingers that this might have some effect but it might already be too late.