2003 Ford Explorer running high RPMs with difficulty slowing down/stopping

I have a 2003 Ford Explorer, and earlier this year I noticed that my car had
began to "lurch" forward as I would come to stops. I took it into the shop
and they replaced the IAC valve.

I drove away and noticed that my car seemed to have a lot more umph to
it. A few hours later, I noticed that my RPMs were running really high and I
would have difficulty stopping (I would be slowing down, but my RPMs
would remain high, making for a lurchy/chunky stop.) If I'm doing a quick
stop, like turning the corner onto a quiet road, I slow down because I'm
pressing the brake, but my car feels like it's about to take off. The best way
to describe that would be if you held onto the back of the shirt of someone
trying to take off running. You've slowed them down by holding their shirt,
but their legs are still moving. Additionally, my car will accelerate itself. I
could slow down to 25 mph, take my foot off the gas, and a half mile later
I'm doing 35/40 mph. I have replaced the TPS sensor, but nothing has
changed.

So this has been going on since last summer (haven't had the funds to take
it back to the shop.) I have noticed in the last week or so, that while it still
does a chunky stop, it will all the sudden stop hard, like a kid who doesn't
know how to properly break. Today, as I was coming to a stop light, it was
doing it's normal, chunky stop, then it all the sudden stopped really hard
then died. When it died the "Check Gage" light came on. I spoke with my
dad, who is a diesel mechanic, and he did not understand why the Check
Gage light would be on (really, my entire car has him stumped.)