ok so i am driving home last night (cant say exact speed cause speedo is not working) but i have a 91 Z28 with 9" rear end with 4:10 gears and a T56 6 speed, i was in top of 5th when i all of a sudden hear a whining noise. i pull over and there is a reasonable amount of white smoke coming from my rear end, the axle housing part. i was aware that i had a leaking seal and that was the cause of gear oil spewing everywhere on my brake and rim. i had cleaned the car earlier in the day and last night there was no oil anywhere as if i was "dry" and burnt what ever was left. today i bought some gear oil and filled up my rear end but the whining is still there.

the whining only is noticeable once im in mid 2nd and from there it increases in pitch as rpm increases. if i put the car in neutral while rolling the noise goes away, and only comes back when i put it in gear and give gas. if i let go of the gas the noise goes away (or what i can hear of it). i really need to know what is wrong as i need to go on vacation this Wednesday with the car.
any possibility it could be my tranny?

i also noticed on the same day, before the whining, that i can not shift down into 5th anymore. it completely blocks me out. i can up shift to all gears and down shift to all but from 6th to 5th. the only way i can get it into 5th is by holding the clutch, putting it in 4th, then putting it into 5, thats what i have to do if i really want to down shift from 6th to 5th. do i have a bad synchro?