Transmission issue 95 chevy 4x4 1500

[95formula383lt1]

I had a issue a few years ago where the transmission randomly didn't want to shift out of 1st or would only do it at high rpm and then when in 2nd no 3rd or 4th. Changed the fluid an filter put lucas in then never had a issue till a week ago. Took the truck through a little mud nothing crazy then drove about 20 + miles no issues then left a gas station had to pull out fast an after it shifted in to 2nd it just acted like there was no 3rd an just free revved. drove home in 2nd gear changed the fluid an filter fluid was clean un burnt hardly any metal on the magnet. A week later its still doing it, speedo goes insane jumps all around even when holding a steady speed, shifts fine when its cold but speedo doesn't act right even when cold, it goes up slow an doesn't go down fast even when u slam the breaks. Un plugged the speed sensor still has a shifting problem. shifts fine if u do it manuely in 1st an 2nd just 3rd an 4th doesn't seem to work. If u put it in over drive the truck shift 1st and second then shifts into third then slams around into diff gears then seems to slip. Its driving me nuts thinking about it and its my DD. we put over 20k miles on it since the last time this happened, trans always acted like it had a shift kit in it an previous owner said it did as well. trans was always clean inside as well as the fluid any ideas?? thank you for your time

95 Sliverado 1500, RCSB, 4x4, 3 inch body lift, 33s, headers, true duels, 1.6 roller rockers, A4.