I am by no means a trans guy. If this question has been answered show me where, but search didn't bring anything up. In D the trans only has 3rd gear. When the trans is warm, then I can manually shift from 1-2-D. R and N both work fine. What is usually the cause for only 3rd gear when in D?
Do you mean that the transmission starts out in third?? And which C4?? Cruise-O-Matic and Select-Shift are different. Cosmo
Sticky gov or a valvebody sticking. 1st thing i would do is to get some trans helper in a can and put it in. That will help with varnish in the gov and body get it warm and run it for 100 miles or so then drop the pan and service it. Now you need to use Type F in there. Hope that helps