My problem is that my disco is very sluggish at low speeds or from a stop. It seems like it struggles to shift and like there is just no real power. But once I get up to say 40 mph + it seems to coast smoothly and pick up when needed. Also noticed that its worse in cooler weather and much better in warmer weather.

Long story short, previously I dropped a motor in and filled the tq. Found that I swapped oil and tranny cooler lines by accident and fed some oil into the tranny. Drained tranny twice since but seems like the tranny is struggling to shift and shifts higher than normal.

This is the first and only disco I have driven and since I bought this one with issues from the beginning I really dont know how a disco shifts normally. Thanks for any info or ideas...

 

It's by no means quick to start with, but if you got oil into the trans, flush it a couple more times. Oil is a lot heavier then ATF, and can easily gum up passages in the valve block, and honestly, I'm not entirely sure what happens if it gets absorbed in your clutches, that was never part of a auto trans course.
I would change it, drive it in all gears until its nice and hot for a while, then repeat. May be worth changing the filter as well.