1995 suburban shifting to quick

i have a 1995 chevrolet suburban transmission is shifting out to quick i have replaced the speed sensor speed buffer and the computer and to no avail still does it serviced transmission can shift it out manually with no problems any ideals

Um you may have already past this point but my 95' taheo was doing some really weird shifting and it turned out to be the battery cable. I cleaned them up and bam it was working fine. I have heard others having similar issues.