tranny? have any? standard?

[~D~I~]

my tranny in my 94 suub doesn't shift out of gear until about 25 miles an hour and about 4,000 rpm's. sometimes it shifts great though. if i'm on the interestet it pulls gret but once you get on it to kick down a gear it slips to neutral? think my clutches are burnt? what would be the problem. what all standard's can i look for? and does anyone have any?