I have a 2004r ran great no problems ever has stage 2 shift kit 2800 stall took top end off and put on new head blower ect

Took car out first time after new parts shifted fine once i hit wot and made boost trans acted funny was like.mile from house parked car took look saw nothing kickdown fine and took out again wont sjift out of 1st to.any gear even if try to manual shift it

 

they have some seafoam transtune I put in my 86 c10 with a th350 transmission,it helped a lot

I think my torque converter was going out,it wouldn't shift out til high rpms and got to were it wouldn't move when I put it in gear,come to find out my ex gfs dad put a hole in the transmission line when he replaced the starter and burnt a hole in the line so it ran out of oil for a long time....

 

Sounds like a bad modulator valve on the trans.