will a 1989 749 coupe transmission fit in a 1990 740 wagon on 1990 Volvo 740

my 1990 740 wagon will not shift out of low gear until it warms up, could this be from a vacuum leak

Asked by for the 1990 Volvo 740
The transmissions don't use vacuum for shift control, so no, vacuum leaks won't cause this. If the fluid level is OK, then check the kick down cable, they start sticking and can cause shifting issues. If that is OK then you may have a transmission with internal issues, and it will need to be checked by a good transmission shop.