New Performance gearbox Pops out of 3rd

Hey guys

I just got a type 1 IRS box rebuilt packed full of goodies, but it jumps out of 3rd gear randomly, sometimes on full throttle, sometimes at cruising speeds, sometimes with no throttle, road surface defiantly isn't affecting it. can take up to 5 mins before it jumps out.

I have it in a type 3 fastback (mounts only on nosecone)
shifter is brand new empi and the shifter housing bush was changed last year.

being a complete rebuild we are unsure what the problem is, any guesses? nose cone maybe?

cheers

Shifter adjustment? or take it back to the builder?

build problem..............................ask Dave Butler.