Muncie M-20 Rebuild kit

[57s67]

My 67 RS/SS was purchased as a roller with the original 350 and M-20 rebuilt, but, not installed in the car.  When I bought the car the previous owner provided me with an invoice for transmission repair.  The invoice included $250 for a rebuild kit with reverse gears.  The car is now on the road and I notice that when in 1st gear and not under load the trans will pop out of gear.  I searched the forum and found an old post mentioning worn sliders (part of synchro unit) could be to blame. 

My question is would a transmission rebuild kit like I described above include the 1st to 2nd sliders?  Any thoughts on other to diagnose problem?

[rszmjt]

Usually rebuild kits do not include the outer sliders. Weird it's jumping out of 1st because usually the 1-2 slider does not wear much on the 1st gear side. Do you have a stock shifter or a Hurst ? May just be a shifter adjustment

[57s67]

New Hurst Competition Plus. 

[Kelley W King]

If your shifter has the shift stops which it should I would back them out. You don,t really need them except racing anyway. If it is the slider I would do both while the trans is out or the "feel" of the 1-2 vesus 3-4 shift will be different.

[rszmjt]

Check the rear shifter stop adjustment bolt (which is for 1st & 3rd ) and make sure it is not screwed in too far when in the 1st gear position, ( check in both positions )  and also make sure shift handle and 1-2 rod is not contacting anywhere . 

[57s67]

All good ideas.  Hadn't thought of backing off the 1-2 stop