first gear high rev problem

[Mudgeumsz28]

well first off i have an 1999 z28 auto with about 35k miles on it and i have been babying it for about the last 5 to 7 months just because i dont want to go though my gas as fast but just recently i have noticed that i am shifting out of first gear at a higher rpm i used to shift around 2000 to 2500 rpms and recently i have be shifting out of first at 3000 to 4000 rpm when this happens i am just giving it light presure on the throttle and when it does shift it slams in to gear like i put a shift kit in it or just used a hypertech programer on it. the only things i have done to my z28 is i put a flowmaster and upgraded the exhust pipes to 3" from the headers back also i installed the slp cold air intake but that was about 6 months ago i didnt have the shift problem until recently i was wondering what may be causing this to happen cuz it is bothering the **************** out of me and does it have to be takin to a shop or i can i fix it myself? if anyone knows what it could be please tell me my friends are stumped and not much help they tell me to wait and see if it gets worse but i would rather fix it as soon as posiable. thanks for your help.

[v-8]

Do you have a 'check engine' light on??? Could possibly be your TPS (throttle position sensor). .

[Mudgeumsz28]

no if it was throwing a code it would be alot easier for me to fix but it is not so i have no idea why it is doing it.

[HMFDZ28]

check fluid levels, but it sounds like either a slipping band or a bad shift soloniod