It's a tbi 350. I actually found out after posting the original question, that the trans is out of a 98 truck, and it's in a 91. From what I've read in other posts, there's issues with pressures and or controllers when late models are used in early model trucks?
I've got a 91 suburban 3/4 ton 4x4 with a 4L80E trans that just in the last 3 days has started shifting in n out of 2nd/3rd. Does it a couple times then drops into od fine. I've never had an electronic trans, always 350, so I'm not sure where to start looking. It's shifted hard, to me, since...