Any idea???

400 Smallblock
turbo 350 with B&M Shiftkit

1st....2nd are fine all day long but as soon as i get up to speed im guessing 30mph+ the engine just dies and almost makes like a whining noise right before it shuts off, it will restart once i drop belofe the 30mph limit.

anyone?

You have a fuel pressure gauge to rule out a fuel problem?Whats the engine set up?

sounds liek trans is trying to engage two gears at once . did you just install the shift kit ? if so maybe a check ball in wrong place or hole not drilled would be my guess. sounds liek the hyd pressure isn't getting where it needs to be to apply third properly. I dout it would be fuel pressure ... sounds liek a trans issue. good luck with it .. let us know :-)