shifting problems

[monte379]

new trans has problems. got trans put in and made a couple of passes down my road and seemed fine. did a couple of rolling launches and seemed fine. then went to the track and discovered a problem. by the way i manually shift the car. trans works fine in the burnout but when i stage the car and power up to 2000 rpm to launch in manual first gear , then launch the trans shifts on its own at about 3500 while i am still in manual 1 st. if i put it in 1st and get rolling 15 mph or so then stand on it then its fine and i manually shift it at 6000. but when launching from a dead stop it will shift on its own way to soon. just got car put back together in time for racing season and now this goofy problem. anybody have any idea's ? i have not had much time to do much checking yet and have only drove the car around the block a few times and then went to the track to discover my problems. seems to shift ok under normal to light driving other than 1-2 seems to shift early but thats not a huge problem if i can figure out how to get it to shift ok during manual shifting. by the way my car is a high 12 second monte with a very mild 350 , 3:73 gear and 2004r in full street trim at 3500 lb. the story behind the trans is that i bought it from a buddy who had it rebuilt with shift kit but he said that it worked fine other than it would not shift at wot. trans had less than 40 miles on it and it had a ct valve body i believe. i bought it from him and i picked up a cz valve body and installed it and i removed the cz governor from my tired trans and put in it. dont have much time or money now just trying do figure out how to fix and get by for now. my plan is to have my original trans that was tired and worn out rebuilt with the good stuff from one of the venders on here as soon as i can save up some money. by the way the original trans in my car had 200,000 miles on it with over 1,000 drag strip passes on it. it was stock other than the shift kit and converter. this was my first 2004r trans that i have had but now i am a true believer in them. it got me many many wins and 2 track season championships. any info or help would be greatly appreciated thanks !