87 300 six with c6 3 spd 2wd

I can go about 15-20mph in 1st, but it doesn't shift and anything faster, the trans slips and no power goes to the wheels... wold that mean trans is done and needs a rebuild or replacement? Or just coverter? Any insight will help. Thank you

 

Have you tried shifting through the gears manually? There could possibly be gunk in the valve body plugging a passage. The filter could be really dirty and restricting flow a little. Before completely writing off the trans try pulling the pan to see whats in there. Put a new filter on and get some fresh fluid in it. See what it does after that. If it still acts the same then id bet the friction material on the clutches are toast.