I'm thinking of pulling my Muncie M21 and sending it out to have it checked.....sometimes it pops out of 2nd or 3rd.....anybody have any idea how much it would cost to have it checked out....are they expensive to work on?......anybody know of anybody in southern california that works on them?.....i also get a bit of vibration also....but its a lot better now that i got the driveshaft balanced.....i was also wondering if the internal gears can be changed?...i have 3:73 gears in the rear and i'm always at 3000 rpm in 4th......i always feel as though i should shift again while in 4th gear

Depending where you're located, Tim Deal Transmissions in Huntington Beach does only "classic" transmissions. Although I have only used him for my automatics, I'm sure he does Muncies too.

Give John Foreman in Anahiem a call at 714-974-5539, he does a good job...
Tell him Crash sent you... Crash

Sounds like your synchros are bad. When it comes to changing out the internal gears for taller ones, I don't know.