Just picked up an 07 sxt, everything seems fine with it, has 120kms on it, I was highway driving today and rpm's seemed high, sitting at 3000 at around 90 km per hour, is this right or is the granny not engaging top gear???

 

That sounds a little high. The CVT trans does take getting used too.
If it was slipping too much, it will usually throw a code and the check engine light will come on.
I would suggest having the fluid changed at the dealer. It is a special fluid and you need a special scan tool to check the fluid level.