I think my commute killed my transmission. What should I look for in my next auto?

My work commute requires me to climb the Cuesta Pass which is a high grade pass of about 3 miles. I started taking this commute about 5 months ago. Now my 2008 Ford Escape is in the shop because the automatic transmission went out. Looks like I'll be in the market for a new car.

I'm wondering if this daily grind may have been too much for the 4 cylinders my trusty Escape was running on.

So, what kind of specs should I look for in my next ride? I like having a mid/small SUV like the Escape. I'm hoping to pay at/under 20K.

How many miles do cars last before they become worthless?

I keep hearing people saying Toyotas and Subarus hold their value and whatnot, yet I owned a Subaru with 250,000 miles and it was a pain to sell(even though it was still in pretty good condition), couldn't find a buyer until I dropped it down to $1000. Everything worked on it and it was reliable.

So is there like a general mileage range where a car becomes "worthless" in a sense that nobody will buy it? If I buy a new car with 0 miles, at what mileage should I sell the car before it is hard to sell? Would it matter between brands(looking at Jeep Renegade, Ford Escape, and a few Toyota models)? 60k miles? 100k miles? 120k miles? 150k?

How to use aux cord w/ no adapter?

Okay so my parents just recently got me my first car, a 2007 Ford Escape, and it has no aux cord. Does anyone know of a way to install one? I would get a cassette adapter but I have no cassette player. It consists of a CD player and a radio. However I do have a couple cigarette lighters up front, is there a way I could use these as a form of audio input?

What is the best way of improving the power of my inline 4?

So my vehicle is a 2011 ford escape xlt with awd and an l4. I would like more power from it. Getting the v6 was not an option. And I will not be getting a different vehicle. I will be using this vehicle for a long while and would like to just give the 4 cylinder a little extra. What is the best way I can go about this? Stock it should have about 171hp. I'd like to try and get it past 200. I do have some money but I can't be putting anything like 4 or 5000 in it. I don't know as much about cars as I would like so anything you can tell me is helpful. Unless you are telling me not to bother then don't waste your breathe. If you know of any parts and you can link it to me for my model it would be much appreciated.

Do these two performance parts do the same thing?

So I'm planning on upping the performance of my truck. And I have come across the two parts.http://www.performancechipsdirect.com/Ford/Escape/ and http://m.autoanything.com/performance-chips/61A1777A0A0.aspx. My question is, do these two parts do the same thing? Or would I be able to install both of them without worrying about any kind of interference. From what I can tell with the installation of both, they are installed in different parts of the vehicle.