Kia Sorento Auto - driving problems

After reading some of the reviews on the Sorento, we still feel that ours doesn't drive like we think it should.   This might be down to our driving, although Jason is a better driver than I am and it's him that has the most issues with it.     Not having had auto's before, it takes some getting used to.

When driving, both solo and towing, is it normal that the automatic gearbox needs to be at 4000 revs before it changes gear?    When driving, we gradually increase pressure on the accelerator but the revs go up but gears don't change.   It seems to be revving for ages before changing - is this right?    When motorway driving, we can't seem to get enough speed to overtake, which is worrying at time when you've already committed to the manoevere.   It struggles to get to even 70 at times (we know is this is the speed limit) but you need to be able to increase speed to pull  yourself out of any danger etc.  

Would appreciate any comments regarding this because as it stands we can't rave about the car like so many of you do and we really would like to 'love' the car as we need to keep for a long period as can't afford to change again  

Thanks in advance for any suggestions