Engine stalls when slowing down, doesn't shift gears when slowing down on 2000 Chevrolet Express 3500

I have a 2000 Chevy Express van 3500 5.7L engine. I just changed the computer, speed sensor, and both solenoid sensors. Flushed the transmission and changed the oil. Had a technician reset the computer as well. Now, van is slow at take off, and when slowing down, gears don't shift and engine almost stalls. Any ideas?

wow. lot going on here. why did you do these things?? what sensors??? there are a lot of sensors. reset?? needs to be flashed, not reset. was the van slow at take off before?? need more info,

Well, I got codes P1336 and P0740. Car didn't start at first, after I changed the computer (or I should say I put in a new computer, since the original was stolen). After making a few phone calls, was told that the computer needed to be reset in order to "read" the "new" car. After it was reset, the van started. But it was not idling enough and would stall. Another code for the shift solenoids came up and I proceeded to change both shift solenoids (1-2 and 2-3). I then flushed the tranny and changed the oil. Does it sound that I need to program the solenoids? I am still getting both those codes, even now. Also, getting code: Torque Converter Clutch Open.
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take van to dealer and have the pcm flashed to restore all points