hello all, i have been wanting a 4th gen fbody for awhile and finally found one and bought it yesturday, its a 1998 z28 has automatic with shift kit, slp intake and longtube headers and custom exhaust. drove it 2 hours home no problem, took it to work today no problem, on my way home i was goin thru a construction zone at 60mph and got out of zone and accelerated to bout 75mph pretty hard, got out of it and was slowing down to speed limit and trans just slips, pulled over checked fluid was full, not burnt or nothing. checked i have reverse, first and second are fine bout third and fourth slip bad... just wanting ideas on what problem could be. ive never been inside one of these transmissions before. wanna know if it will be easier and or cheaper to replace with a used one or rebuild what i have. and also wondering how hard it would be to just change it to a six speed.. thanks for the help im new to this new technology stuff, wondering if i should have stayed with old cars... lol also if i can find a used one does any one work or jus out of an fbody

 

sounds like 3-4 clutch pack, common problem with the 4l60e. Just because it has a shift kit doesnt mean the entire trans was upgraded, most likely the valve body and springs were altered but not the clutches or hard internal parts