2000 Olds Alero problems

Can't figure this one out. 2000 Olds Alero with 3.4L v-6 & auto trans. Has about 134K on it.
The car usually starts fine, sometimes it takes a few attempts.
It idles perfectly and accelerates well. The problem is when cruising at light throttle, the engine starts surging. You can feel it and also the tachometer shows it. Also, the transmission seems to start slipping almost like its getting ready to downshift. If I let off the gas to decelerate, it seems to smooth out. Likewise, if I accelerate it seems to work fine. The speedometer goes wacky too in the same manner. At light throttle it swings erratically from 0 to 60 or so but works fine when accelerating or decelerating. No check engine lights come on and the bulb is working. I connected an Actron scanner to it and it displayed PASS, no codes read. I think the engine & transmission are mechanically sound but something electrical is messing it up. I have heard several horror stories about this
Help would be greatly appreciated
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Possibly the Throttle Position Sensor?

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Though it could be, replaced it, same problem. Also replaced: VSS, MAP sensor, MAF sensor. Never gets a check engine light. Starting to wonder it it's a transmission problem?
Dale

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