4l80e no 4th gear

[Chevy1231]

I have a 1993 chevy c3500 with the 6.5 and 4l80e. When we got the truck the guy told us it would kick out of overdrive. Once we got the engine in it it wouldn't shift unless you got around 3000-3500. But it would go into all the gears but we never drove it ran enough to keep it in the gear for a while. Well we changed the tps and that fixes the high rpm shifts. It now shifts perfect. At first it shifted 1,2,3, 3rd lockup then 4th then lock up. But when you would step down on the throttle some it would kick out of 4th and not go back in unless you stop and shut it off And then go again. well now it quit shifting to 4th altogether and it no longer locks up in 3rd. We took it to a trans shop and when he hooked up his computer it said the truck was in 3rd when the shifter was in 4th. I can't figure this out for anything. It had some bare wires in the wire loom that I thought might of been touching so I fixed those and it didn't help. Then I changed the manifold pressure switch and that didn't help. Could this be a bad solenoid? I haven't had a chance to hook up a scanner to see if it's applying the 4th solenoid. The trans doesn't slip and shifts firm from 1st to 3rd but no more lock up and no 4th. And I looked at the tag and the trans is a 97. So could that be it? Like I said it did shift into 4th before but now it doesnt even try.