shifts with a clunk from 1st to second on 1998 GMC Savana 1500

hard shift with a clunk from 1st to second

Asked by for the 1998 GMC Savana 1500
You may be having some internal transmission problems or the throttle valve cable (if it has one) to the transmission is disconnected. Be sure the fluid's up to level and clean. If this is not helpful, find a transmission shop or a GM specialist for help.
If you want to find a specialist, here's a directory link for you:
where woud i look for the throttle valve cable and would that cause my reverse not to work? THANKS.