Why won't my Taurus accelerate over 25mph?

In my 2001 Ford Taurus, I had my transmission rebuilt a couple months ago and it was
running fine for about a few weeks. Then it would start shaking when I was idling, and
nothing happened, so I got used to that. The last few weeks, when I'm simply
accelerating while driving, sometimes my car won't go. I let off the gas at these times
and try again and usually it will acclerate. Then this past week, when I go to turn my
key in the ignition at startup, the car screeches loudly. I'll try again and then it will
start. Today the same thing happened, but then as I was trying to accelerate up to
speed, I could go any faster than about 25mph. (This is what happened when my
tranny went out before.) I am hitting the gas and it will rev up to about 3500, 4000
rpms, but won't go any faster. Then I stopped, turned off the car, started it up again no
problems, and took it back home (drove home like normal) and that's where it's at.
Any positive feedback is welcome!