i have a 1990 silverado Z71 just got it it doesnt like to shift till i let off a bit and dont get over drive sometimes till i push it too 60 ill let off and it has to freee rev to get back to grabing i just changed the filter and fluid help a lil coul it be something with the valvbody i was gonna try lucas?

 

lucas will help a little.....but it sounds like a valve body or fluid issue