Tach/Speedo acting "WIERD"

I have a 95' HD2500 w/4L80 tranny with 233,000 miles on it. My shift from 2...3 started messing up you know, felt like second went to nuetral, so I replaced solenoids in tranny. Man, She shifted sooooo smooth and I took her up to 70 in nothing flat. Well, NOW I start down the road and my tachometer falls to nothing, My speedometer goes to ZERO, and I have ZERO pull. I stop and kill it, restart and I shift 1,...2,...no 3rd just like before, difference is, sometimes the tach and speedo fall off and I lose everything. Does this sound like a computer board? I was told there was a comp board behind the glovebox with a tranny control board. Is there anything to this? My tranny does not slip, when shifting it is so smooth you don't even feel it shift, but is is Solid Feeling.