Crazy Problems (Long)(Help...hell damn crap!!)

[Sonics2042]

Argh.

I have run into very few problems with my car since I have owned it (besides some alternator stuff), but I fear the times are a changin.

Here's the whole story...
I was going about 110 last night on this one straightaway on my way home. I have gone that fast before and it has always felt like I have plenty of power (speed) left. But last night it felt like I was near my top-end. I didn't really think to much of it, since I wasn't really trying to go faster, but it was odd. Then I stopped over at QFC (a few blocks from my house). When I left I drove for a few blocks and then started going up a hill on the way.

The hill is pretty steep, but nothing I have ever had problems with before. Usually I could accelerate up it no prob. But it never kicked up. I could only go up the hill @ 20 mph @ 1000 rpms even when it was floored. The engine was not racing either. (Good time to mention I have an automatic...). I kept saying "not good, not good, etc..". When I got to the top I turned right and punched it. It went up to 1200 RPMs, but there was no power. When I got in front of my house I tried rev'ving it in neutral and it revved fine (sounded fine and went up to like 3000 RPMs..)

So at this point I know something is wrong, but it's 12ish so there isn't much I can do. Today I started it and hoped for the best. When I turned out of my street I punched it and got some power out of it (just wanted to see something about 2k on the tach...) Everything seemed fine until I got to the freeway. When I got to the freeway I eased the accelerator down (just being careful...) I got to 50 no prob, but just to slowly accelerate from 50 to 60 caused the RPMs to rise above 3500. I could have gotten it higher, but I backed off (I wasn't even accelerating quickly.)

I am thinking this is a tranny problem (felt like I was stuck in like 4th when I was going up the hill, but it felt like I was stuck in 2nd on the highway...)

Any Idea?!?!?!

Car Info:
1990 Mustang 5.0 LX Hatchback
K&N Intake (otherwise stock)
103,000 Miles
Automatic Transmission
Recently changed to synthetic oil...