It could, it just depends how many revs the engine was pulling at that speed. When you say it rev's high and changes gear, do you mean it changes when it's not supposed to? When you take off hard in an auto (Old or New) it will hold first gear longer than when you take off gently, it can also 'kick down' to a lower gear when you're already rolling along at speed and you boot it. This is normal. An auto transmissions can be subject to a condition called slipping. Quite simply this is when the transmission tries to hold a gear, but slips in and out of gear, resulting in the engine revs flaring and usually and big thud or worse, when the car just wont take off. This can be caused by a couple of different things, lack of oil or, simply due for an adjustment of the belts (service).