first post on ls1. i would appreciate any opinions.

the 4L60 shifts very solid from first to second but will not engage at full throttle into third. i have to let off slightly to get it to drop into third. but when it does finally engage it does not slip at all and pulls well all the way through third and into 4th. this only occurs at full throttle and shifts perfectly under normal driving conditions.

the car may have 3.42's or 3.73's just got the car a month ago and have not had a chance to count the teeth on the rear end. could this be a pcm issue
if the pcm was not adjusted or tuned after the gear swap? i am not positive that the rear end has been modified but the mph to rpm ratio seems too high for 3.23's. or could it have more to do with the valve body?

thanks, mike