When you put it in gear you step on the brake, right?  And it dies when you
step on the brake?

Would be worth checking your power brake booster and booster check valve.
Disconnect the hose at the engine, plug it, and see how it drives.  If the
booster or check valve is bad  its a big vacuum leak.

Your problem sounds like it is due to the torque converter.  Sounds like it
is locked up.  I'm not familiar with that transmission, but it may have a
solenoid that locks up the torque converter when cruising, which gives
better gas mileage.  Does your problem only happen after the engine and
trans are warmed up?  IE, after 5-10 miles of driving?  If so, then this
solenoid is the problem.  The solenoid is sticking when it gets hot.  Find
the solenoid and replace it.  Or... just unplug it.  If you unplug it, it
won't go into lockup mode.  It's fine to drive it this way, you just won't
get the small fuel economy benefit.