3000 rpm and 30 mph home eh ??
Sounds like a vacuum leak to the teansmission vacuum modulator..
there is a vacuum line off the front of the q jet .. passenger front..
2" of hose to a metal tube make sure these are snug ...
follow it down to the tranny ..... usually this is where the issue is
the 90 degree hose is usually soft or not snug on the tranny ... poor vacuum makes for late or no shifting ...
I am not a tranny guy ,,,, but my trucks run t 400 tranny ... and I have had this issue b4 also
if any tranny fluid is present IN the hose or on the nipple replace the vacuum modulator as it has failed ...
again I hope for an easy fix for you ,,,, is your carb a q jet ? is your modulator un like the picture and big n black ?
do you still have the steel tube down to the tranny ?
do you still have the clip on the bellhousing bolt for the tube to clip into for vibration wiggle that may have
yanked the hose off ?
thats all I got ... door bells ringin gotta go .............