I have had a chronic problem with my Muncie popping out of gear, if you ever have the tranny out of the car put everything in neutral....there is a whole in the case that you should be able to see all the gears in line. There should be hole about as big around as a pencil lead that lines up all the way through. and if it doesnt align then you should be able to see the problem gear.....i have always had my tranny guy adjust it because i am still a little scared of that area.....or you could have bad shift forks like i did...and continue to have.....i tend to be abusive when i am running her....lol.
I totally hear you about the 4:11's....i was running 4:56's and the way the motor would wind up was a total rush....as soon as i dumbed down to the 3.73's i lost almost a full second off my times....my 60' times were horrible.....but i can cruise on the highway 70mph at 3200 on the tac. better than the 4300 i was at....lol