Brandon's98Z

hello all i got a question about my 4l60e in my 1998 z28. yesterday i took it to the local 1/8 mile track and after about my 3rd trip down the track the trans started acting up, the only mods to the trans are 2800 stall, and a shift kit. So i would launch with the shifter in the 1st gear position, then at about 4k i would push it up into drive, the first 3 trips down this worked great, my car has a cam and bolt ons with hoosier dr's on it and did 7.999 and 86 mph in the 1/8 but like i said after i shifted into drive the following times the trans jumped right into second and then 3rd. it was like it was jump shifting to keep the rpms down under WOT. Im guessing something to do with heat since it didnt do it till the 4th run but im not a trans mechanic. So any questions or advice would be helpful.