1999 Ford Escort transmission problem?

Hi. Heres the story of my 3 month old (used) car. When I got it everything was pretty much working fine (then again I know nothing about cars).
Last week my starter was getting pretty bad so I took that in and got a new one (360 bucks CND later).
Since then I took a 10 hour trip and 3 hours in my engine started reving really high whenever I was driving.
Starts out fine unitl I get up to about 40 km/h and then it revs really high and then changes gear and is fine. Its also really loud now when im going 100 km's when before it was fine.
Never did this before. Theres 172320 kms on it.
It sounds like a standard even though its an automatic.
Now at the 10 hour mark of my trip the engine light comes on almost as soon as I get home. "Check engine soon". And ideas as to what the probelm could be?

Also once during the trip I was going pretty fast and needed to slow down for a speed sign and so I just let off the gas. It seemed fine but once it got down to about 40 km/h all the lights came on and my steering locked up. I pulled over and turned off my radio and vents and sure enough it stalled. Turned it off and back on again and it was fine.

Can anyone please give me insight as to what the hell might be wrong. ONce again I know absolutly nothing of cars and would appreciate anything. Sorry for this being so long. Thanks in advance.